Unfortunately, it does seem true that most of sleep monitoring devices are not very good (I'm hopeful for the head-mounted ones, but I don't have any data).

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.