I’ve used quite a few sleep apps over the last year or two and this is by far the best. You have two options - use it with an Apple Watch or without. If you don’t have a watch, the app correlates the data from when you plug your phone in vs unplugging it, but it also takes into effect when your phones screen is on and subtracts it from your total sleep hours! This is the first app I’ve ever seen do this!
When you use it with your watch, if you turn it into “Theater Mode”, it gets really detailed information about your sleep and tells you when you were in different sleep levels, but with Theater mode all night it uses a whopping 2% battery. It still correlates phone screen time into sleep totals, and subtracts that from your sleep, so you get a much more accurate picture of how long and well you’ve slept. The only bad thing is you have to remember to charge the watch before you get to the point of being in bed.
Probably my only gripe is I think metrics for heart correlation could maybe be broken down a bit more (average HR in REM, average in Deep Sleep, etc), but it does give graphs of where your HR attended out over time so that’s nice.