It seems to do well in head-to-head comparisons with lab-grade tech: https://youtu.be/XIxvGYg2abQ Also, highly recommend https://trainingtodayapp.com for readiness insights. Helped me spot COVID before symptoms set in.
Downloaded as well. Apple Watch seems to be accurate enough with heart rate monitoring in comparison to my Garmin Fenix (with a chest strap) almost to a beat.