I've had this watch since late October after having Watch Active 2... I am not a heavy feature user, and do not use always on, but I consistently get 2+ days out of a charge with Bluetooth on.
SpO2 is always within 1% or exactly matches my medical grade pulse oximeter, HR is very close... as I was a Paramedic, the ECG interests me as I can see more on the dynamic tracing than I expected, even if the watch itself is not officially programmed to report on anything other than A-Fib.
As a tester for MyBPLab, I have been frustrated to get this device set up for BP... it actually worked with all my previous Samsung phones and smart watches starting with Galaxy 9+ and Gear Sport. I expect this function will eventually come through.