I’ve used one for a couple years, and it’s been fantastic. I only wear it at night as a sleep tracker.
After the first ~year and a half of use the battery would no longer hold a charge for more than one day, but I got in touch with their support team and they sent me a brand new ring for free, no questions asked. Now the battery lasts about a week.
In terms of its accuracy as a sleep tracker, obviously no consumer-grade wearable is going to be as good as a sleep study in a lab with full EEG, but I’ve seen anecdotal reports on Reddit of people comparing the Oura ring to the Dreem (an EEG headband), and saying that the two report surprisingly similar sleep phases and durations. It has seemed pretty accurate to me.
The real kicker for me was when I experienced an episode of De Quervain’s Thyroiditis earlier this year and it induced symptoms of hyperthyroidism. Over the course of a few weeks, I watched my resting heart rate overnight rise 60% above my baseline, I watched my HRV and sleep quality overnight plummet, I watched my body temperature increase - this correlated perfectly with frequent blood work that showed extremely elevated levels of thyroid hormones (free T3 and T4). My doctor started me on a beta blocker to control some of the worst symptoms. Gradually as my thyroid recovered, I could watch my overnight heart rate come down, and my HRV and body temperature return to baseline, and use the very accurate data from my ring to help taper off of the beta blocker (with my doctor’s approval).
That specific example aside, in normal daily use I find that the Oura helps me stay in better touch with my body - quantitatively measuring little differences in the status of my body in response to behaviors (food, exercise, alcohol, etc.) that I might otherwise not have even noticed. I highly recommend giving it a try.