The heart rate monitor I can't provide evidence of accuracy, but based on the experience I had with the other features it's safe to guess it's not very accurate. More importantly it's a battery killer and turns itself off constantly.

The interface in total is severely lacking.

Coding custom features is highly unenjoyable.

A large part of it relies on the companion apps which just don't provide much support for the pinetime, especially in comparison to other devices.

The timer/stopwatch/alarm is laughable as it buzzes once and that's it.

I mentioned already that notifications are ugly and bare minimum. Most information is cut off and it can only handle up to 5 notifications in memory before it's cut off and you don't get any more until you check them or it just clears the oldest one. I'm not exactly sure how it handles that because to me it's just unusable.