I get it, at the margin this is probably true but for gross results?
If I drink, AutoSleep lights up like the fourth of July. If I don't, it reports every metric is better. If I drink, SnoreLab lights up. If I don't, it's fine.
Same if I exercise, it's all over the results very clearly.
I'm not claiming they can measure REM accurately but for major life factors they seem pretty damn good.