I ask this as a serious question, I'm not trying to attack you. Promise.
But who the **** needs to know their pulse rate, respiration rate, hydration levels, etc.? I mean, sure, I can maybe think of a few situations, but they are EXTREMELY niche.
Look at the iPod: Everyone loves music, right?
The iPhone: Everyone has a phone and makes calls, right?
These weren't niche products with a very limited user base. I can't remember the last time in my 46 years that I cared what my hydration level was, what my pulse rate was, etc. Not to mention it takes about 10 seconds and ZERO tech to determine one's pulse rate. Why do I need a WATCH to tell me my respiration rate? I can sorta figure that out on my own pretty easily.
I just don't see these health things as being appealing to anyone other than geeks and the aforementioned very small niche uses. And who the heck wears a watch anymore, other than for fashion? The last time I was more than 5 feet from a clock was probably 10 years ago.
I just don't see this as a mass market (as in 10s of millions units shipped per quarter) device. It seems pointless and basically a fad.
That's because you're judging it from the perspective of today's market. Biometrics will become huge in a few years time. These biometric rumors in the iWatch is the first step.
Also, it's not simply the tracking devices that are important. The apps that analyze this data, pull down medical records, and offer you recommendations are also important. I would buy one of these in a heart beat.