I have a sedentary lifestyle, and I bought this to try to help me get fitter.
This activity tracker, like others, obsesses with accumulating data, rather than using that data to suggest ways to improve my health. Data is not an end to itself. Results are, and there have been little.
The sleep tracking is completely wrong. It says I slept for 13 hours yesterday, when I absolutely didn't. It often overstates the number of hours slept, regularly telling me I've slept 10 hours when I haven't.
The stairs tracking is also broken. Every once in a while, it tells me that I've climbed or descended stairs, when I haven't. I always take the lift.
One day, it prompted me to go for a brisk walk, so I did, but it later recorded it as a run. And I can't go and correct it. I get all kinds of useless information about the "run", for example, that I ascended 12 meters. And uses unclear jargon, for example, that my "cadence" is 120 "spm". What's cadence? What's spm? Or that the time of the "walk" is 8 minutes 5.3 seconds, and the "moving time" is 8 minutes 3 seconds. Most of the data it gives me is useless. What do I do with it? What concrete action do I take as a result of knowing that I was idle for 2 seconds during my walk?
The app, and the web site, are too cluttered, giving me all kinds of super detailed information that doesn't lead to a concrete action, and is therefore ultimately useless. At least for me (a casual fitness guy).
I need to charge it sometimes every 2-3 days, which is less than the claimed battery life.
The first day I wore this, I found it so uncomfortable that I couldn't wear it for the rest of the day or the next. That's because the heart rate sensor protrudes from the rest of the device, so the entire pressure of the device rests on a small area, making it uncomfortable and irritating to wear. It left a clear mark on my skin. You have to be very careful to wear this loosely. And, even then, I don't feel like wearing it 24x7, so I have only a partial record of my activity level, and so the conclusions could be wrong.
On the plus side, the screen is more or less legible under all conditions — direct sunlight, shade, indoors, dusk, night. Almost all other devices I've used — phones, smartwatches, ordinary watches — have screens that are legible only under some conditions, not all.