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Thanks for citing the study. Just read through the introduction and conclusion and the Dreem sounds very promising.

After reading Matthew Walker's "Why we Sleep", I currently use the deep sleep percentage metric provided by the Sleep as Android app to determine how well I sleep, and jot it down in a sleep log. The book has given me the idea that deep and uninterrupted sleep is hugely important, but obviously the app is only able to give a crude estimate.

Perhaps this headband would give me better insights into my (failings of) sleep. I hope the parent commenter replies to your message.