Been using my eTrex 30x for the last 4 years. Fine on bike, belt is not stable enough for walking or running (wot, me, run?).
Outputs a GPX with HR in the <trkpt> tags so you can write your own eval prog.
With its permanently-connected 2-pole ECG pickup it'd be nice if Garmin took a leaf out of the Apple Watch's book and detected A-fib, but it's too old hat now for Gamin to bother with. Paging all Garmin hackers...