I didn't exhaustively research but based on un-biased available science I found at the time, any investment (in devices/apps) was not worth time and money. Maybe that has changed.
"For a person to be worrying about their sleep stages is like being worried about the gas makeup of the air you're breathing in," he said."
For study see https://nutritionalrevolution.org/2019/07/20/why-the-oura-ri...
""From EBE analysis, ŌURA ring had a 96% sensitivity to detect sleep, and agreement of 65%, 51%, and 61%, in detecting "light sleep" (N1), "deep sleep" (N2 + N3), and REM sleep, respectively. Specificity in detecting wake was 48%."
Specificity in detecting wake was 48%! If this was a medical test, it would never be approved by FDA."
The NYT article summed up reality for most nicely:
"Dr. Vallat told me that if I really wanted to get better sleep, I should simply try to sleep and wake up at the same time every day — that would help my brain learn how to build a structure for optimal sleep. He also advised making the bedroom a cool environment (about 68 degrees) and as dark as possible; avoiding alcohol in the evening; not checking email or social media right before bed; and asking myself each morning when I woke up, "Do I feel refreshed?""
Stop drinking and watching tv/screens and go to bed on time... don't need an expensive ring or watch to tell you this...
What did the doctor recommend?
But the advice at the end of your post... I'm trying to put it politely - it's insulting rubbish for anyone with moderate to severe sleep issues.
Correct advice, in the absence of actual REM tracking devices, is to go to the doctor - sleep specialist and possibly also a psychiatrist.
If that’s not working then get a full on sleep study, otherwise save your time and money.
Definitely need to take that advice on board!
since then stopped focusing on this kind of variables