RomansFiveEight

One thing to think about. The iWatch is going to require your iPhone to be "present and accounted for" in order to work. It's going to pull it's data, etc., using BTLE on your iPhone. Some very basic apps (like, you know, the one that actually shows time) will work without it, but your heart rate monitor functionality will still require your iPhone somewhere nearby, like in a Jersey pocket or saddlebag. So if you're wanting to use a watch INSTEAD of an iPhone, then you'll probably want a Garmin, et al.

Now as a HUD it'll probably work great. Apple has released an SDK so that developers can create their own iWatch apps. Which means, potentially, Strava, Wahoofitness, MapMyRide, you name it, can have a display option on the iWatch. Which will be cool. That also means that if accurate heart rate monitoring is important, you could STILL use a HRM strap in conjunction with your iWatch.

Personally, I'd love an iWatch, and probably will get them. I might get flamed by the haters but that's okay. There's a lot of cool smart watches out there and I've wanted one for a while. But I've wanted one that looks good (which is 100% subjective). Pebble has some I like. But I really like the look of the Apple watch paired with some of it's bands. And since I use an iPhone it'll be totally integrated with that platform.

An iWatch + iPhone + HRM Strap + BTLE Speed/Cadence sensor would be a pretty cool, full featured cycle computer setup with the right software. The iWatch showing all of the relevant data without draining tons of battery life from the iPhone (or needing to mount the iPhone). And the iPhone recording all the data, coupled with GPS data!

If you're just wanting BPM though, and somewhat more accurate calorie counting isn't important (it isn't for me, I don't trust any calorie counter really. The scale is the most accurate measure of how many calories I've taken in and expended, and I adjust accordingly), then the iWatch will probably work fine!