I checked gadgetbridge, the app I use with the pinetime, and it shows a history of my heart rate and steps and tries to determine if I was “active”. Apparently it does keep track of HR intervals, but it only checks my rate when the watch has the screen active (so whenever checking time, notifications,etc) so random intervals rather than fixed.
I think it’s reliable though. It does what I want out of it and it’s open source, which to me is the main attraction for that price. Idk why they had to make it more expensive for the EU market though. Triple the USD cost, but still. I don’t know if there’s other smart watches that do more or cost less that are also open source and similarly usable?