I find the accelerometer based trackers to be completely useless. I haven't tried a combo pulse/accelerometer type that should be better but I am doubtful.
I use a Contec CMS50I pulse oximiter on occasion in addition to the sleep log. I can determine when I first get to sleep based on my pulse but otherwise it doesn't help other than that I can tell when I take it off. My estimates of when I get to sleep have always been close, although I'm guessing this might not be the case for most people.
For the sleep log, I record when I get in and out of bed (rounded to 15 minutes), when I guess I get to sleep and wake up (rounded to 30 minutes), time in bed, estimated sleep, any medications I took before bed, time I use light therapy in the morning, and any notes I want to remember about how I slept (or anything else since I don't otherwise keep a journal).
I'm not convinced sleep tracking is actually a good idea for most people (or necessarily anyone as a regular thing). The negative of a sleep log is that thinking about when you get to sleep and wake up enough to make a guess will wake you up a bit. The trackers mostly don't seem accurate enough to be all that useful. I'm not sure what most people would do with the information; it seems mostly helpful to compare different sleep medication or practices or to convince yourself that you are getting more or less sleep than you think. I suspect that just writing down in the morning how well you think you slept, how you are feeling, and maybe when you got in and out of bed might be at least as useful as anything more elaborate.