Apple's eGPU developer's kit is promising, but what gets delivered in the future is anybod...
After hammering on Apple's external GPU developer's kit for a week, AppleInsider discusses the hardware, the technology, and what needs to happen in the future for adoption of the concept by Mac users.

There are a few key points we just want to get out of the way, up front. Yes, the Sonnet eGFX Breakaway Box 350 at the core of the developer's kit runs on Sierra -- with relatively simple hacks required to get it going. No, the AMD RX 580 video card in he kit doesn't.
Yes, we did benchmarks. No, they're not really relevant, believe it or not.
Thunderbolt 3 will hit you for about 10 percent of any given card's maximum potential performance-wise. Connecting through Apple's $59 bi-directional Thunderbolt 3 to Thunderbolt 2 adapter, Thunderbolt 2 will chop off about 20 percent, and Thunderbolt 1 will kill nearly 50 percent.
Don't loop back the video to a MacBook Pro's display with hacks you find, because that's about another 50 percent, in addition to the overhead from Thunderbolt. Yes, that means you get almost nothing out of a Thunderbolt 1 system looping back.
Plus, there's no good way to compare Metal to Metal 2 in High Sierra today. The AMD card in the developer's kit doesn't work in Sierra, and the Nvidia cards we're using in Sierra don't work in High Sierra right now.
That out of the way, let's look at the AMD RX 580 card, the enclosure, and how this all works with macOS.

The enclosure is an unmodified $299 Sonnet eGFX Breakaway Box 350, which isn't shipping outside of this developer's kit until late June. A $349 version will be available for cards that need more power in July.
The Sonnet box is quieter using the same cards than all of the other enclosures we've tested. Fully stressed, the enclosure hit 51 dBA at three feet from the case, versus 71 on the Razer Core and 64 dBA on the PowerColor Devil Box. Idle, the Sonnet enclosure is 40 dBA, with the the Devil Box peaking at 44dBA, and the Razer Core maxing out at 49dBA.
As an added bonus, the tidal volume of air ripping through the Sonnet enclosure is less, with the case utterly lacking the ability to move a box of Kleenex, like the Razer Core did.
For comparison, A 2016 MacBook Pro under load is about 36dBA and about 31dBA idle or under light load.
During the course of our testing, we connected the Sonnet eGFX Breakaway Box 350 connected to a Acer CB281HK 4K display by DisplayPort downstream of a series of Thunderbolt 3 docks, and still had no performance issues or bandwidth limitations on it, even when assaulting the dock with network and mass storage calls.
Performance dipped a very little bit with a second Acer B286HK 4K display attached to the dock. If this is a use-case you're considering, plug in the 4K display not to a dock in-line with the eGPU, but to the computer directly -- all performance hits evaporate on a 15-inch 2016 MacBook Pro.

Power demands aren't small. If you're used to your laptop sipping at power while cranking away at your work, the extra 300W plus that you're sucking down might make an impact.
That, and consider ventilation issues. While we already mentioned that it isn't moving a high volume of air, it does need to be vented and the air coming out of the case is pretty warm.
On the other hand, if you're used to the slab-side Mac Pro tower, then power or ventilation issues from the enclosure aren't a big deal.
The restrictions are more-or-less universal to both the third parties, and Apple's use of the technology. We'd like to see Apple eliminate some of them in the build-up to a spring 2018 release for the general public, but we're not sure what Apple's plans are for actual user support, and supported technologies.

What we don't want to see is anointed case and card combinations. An open case that adheres to the Thunderbolt 3 protocol, and a wide selection of compatible video cards to choose from will help the daring users who want to give it a shot.
That way, the Final Cut Pro crowd can get the optimized AMD cards, and the Adobe gang can get Nvidia, and everybody can live happily in an environment optimized for what they need. But, a burly video card regardless of manufacturer is still faster than the Radeon Pro discrete chipset included in the MacBook Pro, even if not optimized.
We feel that support of clamshell mode is a must for the release. While we're dreaming we'd also like to see Apple play around with the technology a little before release, and allow cases with a pair of Thunderbolt 3 ports, like the Devil Box, be able to pass the accelerated signal back to a connected MacBook Pro, or iMac, or use two ports for a SLI case holding two beefy cards operating in tandem to drive an external monitor.
But what you get is what you get. We know that Apple reads AppleInsider, but we just don't know how much they listen.

There are a few key points we just want to get out of the way, up front. Yes, the Sonnet eGFX Breakaway Box 350 at the core of the developer's kit runs on Sierra -- with relatively simple hacks required to get it going. No, the AMD RX 580 video card in he kit doesn't.
Yes, we did benchmarks. No, they're not really relevant, believe it or not.
Thunderbolt 3 will hit you for about 10 percent of any given card's maximum potential performance-wise. Connecting through Apple's $59 bi-directional Thunderbolt 3 to Thunderbolt 2 adapter, Thunderbolt 2 will chop off about 20 percent, and Thunderbolt 1 will kill nearly 50 percent.
We'd like to see Apple play around with the technology a little before release
Don't loop back the video to a MacBook Pro's display with hacks you find, because that's about another 50 percent, in addition to the overhead from Thunderbolt. Yes, that means you get almost nothing out of a Thunderbolt 1 system looping back.
Plus, there's no good way to compare Metal to Metal 2 in High Sierra today. The AMD card in the developer's kit doesn't work in Sierra, and the Nvidia cards we're using in Sierra don't work in High Sierra right now.
That out of the way, let's look at the AMD RX 580 card, the enclosure, and how this all works with macOS.
The good
The RX 580 card included in the developer's kit is as expected, a reference-design card from Sapphire. Roughly speaking, outside of an enclosure, it is a 6 tflop card, where there the Radeon Pro 460 and 560 built in to the 2016 and 2017 MacBook Pros respectively are right around 1.9 tflop as installed. So, the RX 580 delivers about triple the raw computing power of the discrete GPU.
The enclosure is an unmodified $299 Sonnet eGFX Breakaway Box 350, which isn't shipping outside of this developer's kit until late June. A $349 version will be available for cards that need more power in July.
The Sonnet box is quieter using the same cards than all of the other enclosures we've tested. Fully stressed, the enclosure hit 51 dBA at three feet from the case, versus 71 on the Razer Core and 64 dBA on the PowerColor Devil Box. Idle, the Sonnet enclosure is 40 dBA, with the the Devil Box peaking at 44dBA, and the Razer Core maxing out at 49dBA.
As an added bonus, the tidal volume of air ripping through the Sonnet enclosure is less, with the case utterly lacking the ability to move a box of Kleenex, like the Razer Core did.
For comparison, A 2016 MacBook Pro under load is about 36dBA and about 31dBA idle or under light load.
During the course of our testing, we connected the Sonnet eGFX Breakaway Box 350 connected to a Acer CB281HK 4K display by DisplayPort downstream of a series of Thunderbolt 3 docks, and still had no performance issues or bandwidth limitations on it, even when assaulting the dock with network and mass storage calls.
Performance dipped a very little bit with a second Acer B286HK 4K display attached to the dock. If this is a use-case you're considering, plug in the 4K display not to a dock in-line with the eGPU, but to the computer directly -- all performance hits evaporate on a 15-inch 2016 MacBook Pro.
The bad
The enclosure delivered 60W of charging power. This isn't enough for the 15-inch MacBook Pro now, as clamshell mode isn't available at present. The beefier Sonnet enclosure for higher-powered cards rectifies that situation and provides full power -- but isn't an option for the developer's kit.The ugly
Once again, as is the case with nearly every Thunderbolt peripheral we've tested, the included cable is about 18 inches long, and near useless, given that the port on the dock is on the rear of the case. Count on $50 or more on top of the kit's or enclosure's price to get a usable length active cable, capable of full data transfer speeds.
Power demands aren't small. If you're used to your laptop sipping at power while cranking away at your work, the extra 300W plus that you're sucking down might make an impact.
That, and consider ventilation issues. While we already mentioned that it isn't moving a high volume of air, it does need to be vented and the air coming out of the case is pretty warm.
On the other hand, if you're used to the slab-side Mac Pro tower, then power or ventilation issues from the enclosure aren't a big deal.
...and the sequel
Without relying on third-party hacks, Apple's eGPU implementation in High Sierra is very much in its infancy. There are a bunch of restrictions, including the aforementioned lack of clamshell mode, no current support for HDMI audio, no sleep support for the attached Mac, and a few other things. These might be a big deal for you, they might not.The restrictions are more-or-less universal to both the third parties, and Apple's use of the technology. We'd like to see Apple eliminate some of them in the build-up to a spring 2018 release for the general public, but we're not sure what Apple's plans are for actual user support, and supported technologies.

What we don't want to see is anointed case and card combinations. An open case that adheres to the Thunderbolt 3 protocol, and a wide selection of compatible video cards to choose from will help the daring users who want to give it a shot.
That way, the Final Cut Pro crowd can get the optimized AMD cards, and the Adobe gang can get Nvidia, and everybody can live happily in an environment optimized for what they need. But, a burly video card regardless of manufacturer is still faster than the Radeon Pro discrete chipset included in the MacBook Pro, even if not optimized.
We feel that support of clamshell mode is a must for the release. While we're dreaming we'd also like to see Apple play around with the technology a little before release, and allow cases with a pair of Thunderbolt 3 ports, like the Devil Box, be able to pass the accelerated signal back to a connected MacBook Pro, or iMac, or use two ports for a SLI case holding two beefy cards operating in tandem to drive an external monitor.
But what you get is what you get. We know that Apple reads AppleInsider, but we just don't know how much they listen.
Comments
the fact that they killed the MacPro line with the horrible trash can Mac and have not refreshed the Pro lineup since then tells me a lot. The new iMacPro is cool, but it's still not what audio/video pros like me really want or need.
my old MacPro 5,1 is the best pc I've ever owned. I would rather they revive that lineup/design if I'm going to pay $5k for one. I want to be able to install my own hard drives, video cards, RAM and other things myself. You can't do that in an iMac.
if they announce a new version of the trash can MacPro, I will be moving to a windows pc that has the requirements I specify.
plus, while I love my iPhone 7+, it's not really helpful to remove the audio jack as I used my iPhone as an instrument in my music. The little adapter sucks and got lost in 2 weeks. They want 48 bucks for a new one. Screw that.
also, why does everything have to be so damn expensive? They have BILLIONS in the bank. How about boosting profits by dropping prices and selling MORE UNITS?
I leave the adapter on my one pair of wired headphones that I use at the office, and my wireless Beats are all I use at home. I understand that functionality was lost, but you're talking about an adapter that was included, and can easily remain attached to your cable if needed.
Ever since Thunderbolt was announced people have been posting how cool it would be if you could plug an external GPU into your laptop or AIO and leverage a new powerful GPU for gaming sessions. I thought that's what this thing was for.
I am waiting for the Sonnet 500W version to be sent from B&H Photo but I'm tempted to cancel the order if I can. I had originally purchased assuming that it would just work. Currently I'm plugging my mid-2015 MB Pro with just discreet graphics (it can only power a 4k and second monitor even if in clamshell mode unfortunately) into a OWC tbolt2 dock, and then using a software USB adapter to power a 3rd monitor. I had an old 760GTX not being used and assumed I would have the ability to use the Breakaway Box to basically replace that setup - I plug my 4K and 2 24" monitors and then I can close my macbook and work with the monitors being powered off the graphics card. I'm starting to think it's more of a PITA than it's worth? They definitely need hot pluggable and clamshell enabled asap for this to be viable.
"Don't loop back the video to a MacBook Pro's display with hacks you find, because that's about another 50 percent, in addition to the overhead from Thunderbolt."
So with Thunderbolt 3, you'll lose about 60 percent of the processing power of the external GPU if you hack it to loop back to a MacBook Pro internal display (or an iMac internal display). Hence my comment about the iMac needing a second screen with lower PPI next to it to fully take advantage of this.
My point still stands: Unless you're developing or playing VR on an iMac, the best and most likely use case for an eGPU (with Apple's current method in High Sierra) is actually docking your MacBook Pro and using an external monitor.
Here's where things get really frustrating: The highest PPI mass-market external displays you can currently buy? LG's UltraFine 4K and 5K displays... which don't work with eGPUs because they only accept USB-C and Thunderbolt 3 input. This will get better once there are better and more ultra-high-resolution displays on the market which accept mini DisplayPort input, and I have to believe they are coming at some point. Until then, you'll have to settle for a separate screen that has a lower pixel density than your MacBook Pro or iMac display, and that seems like a major step backwards for such a significant investment.
But hey, it's all in beta. Give it time. Apple isn't launching this feature publicly until 2018.
You''re right in one regard, though. I wouldn't want to attach this to a cheapo laptop.
tl;dr: feel free to not buy it, and it may not be a cost-effective upgrade, given that the enclosure is around $300! But, you're mistaken about performance.