RyderDA

I converted my bike using a Swytch kit a few years ago. It took me longer to move the tire & tube off the old rim and onto the new one than to install the rest of the kit! It's a great kit with the biggest limitation being Swytch is mostly designed for urban commuters in fairly flat (UK) cities, riding on pavement. It's got plenty of oomph to get you up basic hills (and make headwinds go away), but the range is limited (especially with the latest power packs). I got an earlier power pack which is MUCH bigger, and can do 50-70 km on a charge (with hills). Like all rechargeable batteries, the range I've been getting over the years has been decreasing compared to when the battery was new. The new systems have much less range; they even made a power pack a while ago with just 12 km of range, but it was basically the size of an thick iPhone (but it charged in just 30 min).

Swytch has been great with service. I don't ride in the winter, so my battery sits idle for 5-6 months. Even following their procedure to charge every 3 months, it was totally dead after the first winter. Swytch sent me a new one. 

It's a bit of a pain to wait for shipping, but that keeps the cost very low. I ordered mine in October. It was put on a ship in China in January, and I received it in Canada in May.

The big advantage to kits like Swytch is you don't have to toss a perfectly good bike (or frame) as you would if you bought a new e-bike. Non-electric used bikes have crashed in value; they're basically worthless where I live. In addition, most e-Bikes have only ~7 gears. I still have all 21 gears of mine.

In answer to the comment above, there's so little weight added to the front wheel that braking is unaffected. If I'm riding up steep loose gravel at a high power setting, yes, you can feel the wheel spin as it tries to grip. I have actual mountains where I live, and ride on actual mountain bike dirt trails with consequential 20% grade hills. It's not great for that.

Switching power support levels is done pushing buttons on the battery, and would be MUCH better done from some kind of thumb switch on the handlebar.

If you want a true electric mountain bike, a Swytch kit isn't for you. But if you do a lot of paved road/trail riding, and a little gravel riding, as long as you're aware of the battery capacity, you'll love a Swytch kit.