I bought a Band 2 back around February. On paper it seemed like it did everything I'd want. GPS, HRM, etc. However, when I went to take it cross-country skiing, I found it only had two GPS modes: run and bike. Well, I run, and bike, and ski, and I didn't want my skiing data polluting my running or cycling data. So that was a pretty strong blow against it. Good on paper, not really designed for my use case at least. Then when I went on a not-particularly long day of skiing, it couldn't make it through the day without running out of battery. That was the end of the road for me, and I returned it.
I now have a Garmin Vivoactive HR on my wrist. It actually does everything the Band was supposed to do, and much more. The screen isn't as bright, but on the other hand it's waterproof and has 5-day battery life. Plus Garmin's app and web site are much better and deeper than Microsoft's.
I wanted to give Microsoft a chance to succeed, but while they had all the buzzwords, for meat least it didn't gel into an actually usable product.