I own a Bangle.js 2 and really wanted to like it. I have a pretty high tolerance for awkward workarounds to maintain a moral high ground, but it just was no fun. The touchscreen tended not to respond as expected - it seemed to regularly, but not always, have an input offset of around 20% of the screen. My first one's button broke despite minimal use due to the above - only really wore it as a novelty (it was replaced to be fair). The app ecosystem requires attention to stop different apps intefering with each other. The Gadgetbridge connection wasn't especially reliable for me. Etc.

I finally gave up when I found the tiny magnets which hold the charger on to the watch had fallen out and were lost when I went to charge it one day.

I own a BangleJS2. I don't use the fitness features but it works quite well on Android with GadgetBridge, a pricacy-focused smartwatch management app, and the OS and apps are all open-source. It was a bit rough around the edge when it came out, but so far it's been quite stable. I even made some PR fix some annoyances.

You can check all the available apps here, there should be something that will monitor which fitness activities you want, and the data can easily be exported from Gadgetbridge

https://banglejs.com/apps/