I used an Oura Ring most of last year. The hardware was very nice, but man that app is a dumpster fire and you can't use the ring without it or the subscription. What a shame.

The advice it gives is like shaking a magic 8-ball. It flags all exercise as "high physiological stress". It's somehow worse at tagging the activity than the rock bottom cheapest smartwatches. The blood oxygen is incorrect half the time and riddled with artifacts. It fails to detect naps and the first and last hours of sleep, so it insists you're in terrible shape with high sleep debt.

Yes, I had the correct size ring and even tried jamming a spacer in there to get it even tighter than it already was. Also tried other fingers, etc. The only solution that worked was to wipe all data every once in a while so that the stats wouldn't drift so much.