If I do cardio exercise for an hour and am measuring my BPM the whole time, a little less than 20% of the battery is drained. They changed the BPM algorithm in the latest Infinitime update, not sure what the battery hit was in the old one.
I turned off Bluetooth and put the watch on the shelf five days ago, the battery drained maybe 14% over that time. I mainly use the watch to measure my BPM, but it can do other things (measure steps walked, get notifications from an Android phone, stopwatch, tell time of course, a somewhat weak flashlight app, it even has games like 2048 and Pong).
On Android there is a Sleep as Android app, which I have never used, which says it integrates with PineTime. Reading what people on the net say, some have been happy with it, some have encountered problems. I have never tried to get sleep readings on Gadgetbridge and don't see any talk about Pinetime and Gadgetbridge for sleep on the net. I know someone who has a Fitbit where the sleep measurement from watch to Fitbit app is very extensive, and even tries to estimate when someone is in REM sleep and such - Pinetime doesn't have anything like this yet.
To me it's a $27 (plus shipping) hackable watch that does the main thing I want it to, measure BPM. As people code for it, it will probably get more capabilities - someone already improved how it measures BPM in the latest version of Infinitime by doing some fast fourier transforms and the like. Some of the more expensive watches seem to have more capabilities, but I like it for my purposes.