I have a biofeedback hobby and have done experiments with HRV. R-R intervals per pulse are quite useful. 5s reporting intervals are too long. Of course I use a EKG Polar Monitor although the literature seems to think a quality PPG or even an advanced radar-based system ought to perform well enough.
Pixel Watch 4 seems to perform quite well as well it seems.
I have a biofeedback hobby and have done experiments with HRV. R-R intervals per pulse are quite useful. 5s reporting intervals are too long. Of course I use a EKG Polar Monitor although the literature seems to think a quality PPG or even an advanced radar-based system ought to perform well enough.