Earlier quoted context omitted.
They still don't have the regular oxygen monitor mode back yet because of a patent dispute. That might be part of it.
That's only in the US, right? (My flimsy understanding is that blood oxygen measurement is how at-home sleep studies work?)
I did one of these and it was the worst night of sleep I ever had. It's somewhat invasive. Meanwhile, I sleep with my watch every night with no problems.