From what I can tell, none of these accelerometer-based methods work at all and the companies pushing these as sleep trackers are making false claims.
Setting the sensitivity to "normal" just raises the noise floor in their filter so high that it obscures the data.On sensitive, I've never had issues with it identifying "sitting" as "sleeping", yet it still effectively tracks my sleep (including periods of wakefulness immediately pre- and post- slumber in bed as well as mid-night disruptions that wake me up). This suggests that I'm getting pretty good data (though not equivalent to a sleep study with ECG/EKG equipment). In this case, "good" is good enough for my uses.