I've had my Band since Thursday evening (November 20) and am happy with it overall. At first, it was undercounting my steps, but I've figured out that I was walking slowly and softly -- it would appear that it doesn't detect those as steps, which probably helps it to avoid overcounting activities that aren't steps. Overcounting was always a problem with my FitBit Flex, so this is a nice change.
Getting started was quite easy. Plug the Band in, download the Health app to my Lumia 1520 and log into it with my Microsoft account, then follow the instructions on the Band to connect it to the phone.
Hardware-wise, it's bigger and heavier than the Flex, but it's smaller than any men's watch I've ever owned and about the same weight. I've seen some complaints about the clasp being difficult to use, but haven't experienced any problems with that. It's been comfortable to wear, though I haven't figured out how snug it should be to work most effectively.
The software on the Band works well and is nicely designed for a minimalistic device like this. I like being able to get notifications on my wrist rather than reaching for my phone whenever it dings. My only gripe about notifications is that clearing one on the Band doesn't clear it on the phone and clearing it on the phone doesn't clear it on the Band. I guess that's a complaint about all wearables right now, but I'm hopeful that Microsoft will solve the problem.
The other gripe I have is that when I engage Quiet Hours on my phone, I still get notifications on the Band. Since the point behind Quiet Hours is to silence those notifications so that I can concentrate on that meeting I'm in or that complicated bit of code I'm working through, having them buzz me on my wrist is kind of counterproductive. Even if the "other" smartphone platforms don't have some form of Quiet Hours, Microsoft can certainly build the capability to "hold" notifications into the Windows Phone version of the Health app.
Speaking of the Health app, it's easy to use. I haven't used the workout/guided workout pieces of the Band software, so I can't say anything about that part of the Health app. I find it strange that the "Sleep" piece of the app doesn't show any history -- only the last night's stats. The "Steps" and "Calories" tiles have the ability to flip between today's information and the past week's summary. To see prior sleep stats, you have to tap the menu button in the upper left, then select "Activity History".
I've been looking at some of the guided workouts and like they way they're set up. There are videos of each individual exercise and there seem to be a lot of workouts to choose from. I've found several that look interesting.