Had the Oura ring for about 2 months now and it's been helpful seeing the amount of data it would give you. Sleep is something I've been wanting to focus on improving, so I've been using the ring to track trends in my sleep habits, see how things like a late meal impacts it, as well as using it to track my activities too. There's a manual add for workouts which is helpful as I don't wear my ring when using weights to prevent scratches. It's also super simplistic which I love! I usually wear a size 5 ring but the 6 fits me - if you have small fingers, just be cautious during the winter time. My fingers constrict when it's cold out and the ring becomes pretty loose, so just be careful.
The ring breaks down your sleep data so you can track light, deep, REM, etc. I use it more to see how my sleep has been trending, as some times I'm not sure how accurate it is e.g. it'll tell me my latency (how long it takes you to fall asleep) is <10 min. when on certain nights I know it's taken me an hour to fall asleep.