Recent theVerge.com article says the Apple Watch is sending too many people to doctors for further investigation (only ~10% had actual cardiac problems). see https://www.theverge.com/2020/10/1/21496813/apple-watch-hear...
Also the main new feature of the Apple Watch 6, blood oxygen monitoring, was reported as unreliable in theVerge.com review: https://www.theverge.com/21496141/apple-watch-series-6-revie...
and a Washington Post article put down the Apple Watch and the FitBit Sense's blood oxygen monitors:
https://www.washingtonpost.com/technology/2020/09/23/apple-w...