I won't be buying one as I have only had my "Band 1" for a couple of months but it has offered a fascinating insight to my health thus far. I am disabled and have no use for 'guided workouts' or cycling/running tracking but I can track my heart rate throughout the day and night (which has helped me isolate and tackle some very awkward sources of stress) and can use the sleep-tracking data to gauge how certain activities and medication are affecting my sleep patterns.
I was sceptical about all of these sorts of things and although I wouldn't want a smart-watch having a "half intelligent watch" that can do all of this tracking and combine it with notifications, Cortana and a few apps is quite nifty.
The lack of a decent glass on the first version of the band is a glaring oversight, though. It's scratched to buggery despite me a) looking after it and b) not being outdoors a great deal.
Biting the hand that feeds IT
