I've had a Withings Steel HR (was briefly owned by Nokia) for 5 years and would recommend it to anyone. About £150 new, still achieves a month plus battery and in that time all I've done is change the band a few times.
Upsides: Month long battery (doesn't use a standard USB cable, but it reaches full charge in about an hour), basic activity tracking, smart alarm clock (which I absolutely adore[0], haven't used phone's alarm for years), no subscription needed for any of its features.
Downsides: glass is not scratch-resistant (mine's full of scratches), getting data out of via API is not trivial, and the screen itself is annoyingly small (it can fit like 10 characters).
For the past two or three years I did look into other options a couple of times, but they all either don't have any additional actually useful features, or if they do their battery barely lasts days. I don't see myself switching to anything else for the foreseeable future, unless Withings goes out of business of course.
[0] Instead of telling it "wake me up at 9am", you can tell it "I need to wake up at 9am, but 8:30am is fine if you detect my sleep is weak". It wakes you up by vibrating. Quick press of the only button on the watch turns the alarm off, longer press snoozes it for 10 minutes.
EDIT: I also discovered by accident that it still "works" even with 0% battery. I forgot to bring that special USB cable with me on some trip and I still used it to track time/steps for days until I returned home.
Is it hackable? I don't want to faff about with proprietary bloated apps, I just want to interface with it to read sensors/write data via whatever application I choose.
