I don't have a recommendation but I have experience with a few.
fitbit
I have a fitbit. While I like it for other reasons, I wouldn't recommend it if your interest is sleep. In my opinion, the sleep tracking is the least compelling of all its features. I have an older model that normally goes in your pocket with a separate wrist sleeve just for sleep. But most of the functionality is accessible via the app or web, through which all their devices share most of their features. All the sleep data is analyzed on the app/web after syncing a complete sleep session, not in realtime. It wasn't comfortable on my wrist (but YMMV), so I leave it in my pocket as I sleep. Conveniently, all my sleep clothing has pockets.
Sleep stages?
The fitbit uses motion detection to classify your sleep state in the non-scientific categories of sleep, "restless," and awake. Sleep is no movement and the difference between restless and awake is, I believe, a threshold of magnitude or duration of movement. From my experience, restless/wake will sometimes show false positives during REM, but only in isolated spikes, so there's not much useful correlation.
Analysis
It computes "sleep efficiency" which is just sleep/total time and can't guess at the more robust definition of sleep efficiency which should be (deep+REM)/total time, or in other words, excluding light sleep. That was all mildly interesting to look at for about a week, but didn't reveal anything new beyond what I learned from the Zeo (see next section), so I don't bother looking at it regularly. The one chart I look at is hours of sleep broken down for the past 14 days, mostly just to gauge any recent trend. But actually that data is just when you start and stop the timer, which doesn't leverage the motion detection at all, so you could do that chart with any spreadsheet.
Alarm
It has a vibrating alarm, which I quickly stopped using. To judge the vibration by analogy to sound and musical instruments, I would have wanted a low rumbling double bass, but these little devices are like tweety little violins. And I suspect that's more a function of the devices' physical size, not features. The alarm is set for a fixed time and there's no way for the alarm to be triggered in a smart way by the sleep state (and perhaps you wouldn't want to, as the motion-based detection is a poor approximation).
Conclusion
To be clear, I'm not saying fitbit misrepresents itself in anyway. Just that fitbit's sleep features are a rather shallow afterthought of its bread-and-butter motion tracking that doesn't offer much uniquely specialized for sleep. It's geared toward quantifying overall sleep quality with the sleep efficiency calculation on a day-to-day basis. For someone trying to improve their health and time management? Copacetic. For lucid dreaming or anything in the realm of neuroscience? Meh.
Zeo / headband type
Before the fitbit I had a Zeo. I guess they are out of business now, but maybe there are newer similar products that work with a headband that detects electrical activity. This type of tracker splits sleep into stages of light/deep/REM/wake. It was very interesting but in the end it was more of an expensive curiosity that anything else. I personally found it to be accurate enough (or at least consistent in deception), but other users have long been skeptical of the accuracy of these devices.
Alarm
It had a smart alarm, which I used for the hell of it, and it might have even functioned correctly according to its algorithm, but it made no appreciable improvement to the quality of my sleep or morning mood (another YMMV). I also tried using the smart alarm to wake me for an ideal WBTB, but in the end it was more reliable to wake naturally without an alarm after a dream. Finally, I thought I could perhaps use the smart alarm for EILD, but it's really not designed for that. It would have needed to be more programmable, or at least specially designed for lucid dreaming like a proper EILD device.
Conclusion
Over time, the headband would lose accuracy to the point of useless and needs to be replaced, at some additional expense. I stopped using the Zeo after the headband was kaput. I don't regret buying it and I am fortunate that the cost was not a concern for me, but I wouldn't recommend it or any similar electrical headband sleep tracker as anything more than a curious pastime for an enthusiast with money to burn.
sleepbot
For a while, after the Zeo and overlapping the fitbit, I used sleepbot. It's just a phone app that uses the phone's accelerometer, which I know the OP excluded but I'll mention it anyway. For a while, I found it useful just to record the start and end times of my sleep, without caring for the motion detection or alarm features. For that purpose, its charts synced on the website are more interesting than fitbit's. But I have since replaced that with a plain old calendar with my waking and sleeping activities all together. It was also useful for the sound recording function because I wanted to know if I snore or talk in my sleep. (Turns out I don't.) But for that purpose, I only needed about a week to make my conclusion.
Opinions
Here's my opinion and please take it only as my opinion and not an authority or specific recommendation.
Cheap experiment
Practically, the best value of tracking your sleep state will be to do an experiment for maybe a week to a month, if you have the discipline to stick with it. For that timespan, it seems most economical to me to just go with the free or cheap phone app and tolerate however awkward it might be because you're only going to do it for a little while anyway. They will all produce the same data, perhaps with varying accuracy, based on the less-than-ideal motion-based measurement. If there is a difference, it will be in the usefulness of the data charting. After the short experiment, you will have learned if you toss and turn, snore, or sleeptalk. And you might learn approximately when you wake between REM cycles, but more likely you will learn that either: your cycles are very regular (which you could have guessed without the tracker) or very irregular (which is useful to know, but now knowing it, further tracking beyond a few weeks won't reveal anything new).
Medical condition?
If you suspect you have a medical condition that needs treatment (like sleep apnea) then consult a doctor.
Enthusiast with money to burn?
If you really want to geek out on the light/deep/REM breakdown and perhaps experiment with how they are affected by supplements, then I suspect motion-based technology won't be sufficient, thus favoring the electric headband kind. BUT, while that data makes an interesting chart, I opine that it doesn't have much practical value other than merely confirming what you can already learn from current scientific models and what you can already judge subjectively about your sleep quality.
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