The comments referencing quantified scientists do so in a somewhat negative light. But it should be noted that in his research, he points out that the oura is one of the top trackers for sleep[0]. This is not the only video that he praises the oura for being pretty damn good based on other devices.
For sleep phases and mediocre oxygen levels and bad HRV readings. And on his blog he says he does use it for his sleep tracking, so yeah. I'm not saying it's terrible but for sp02 I can confidently say it's terrible. I use actual nighttime pulse oximeters from Wellue which is also a (larger) ring form factor[0]. and I can see the large dips in O2 for example, the Oura will not detect this despite going into the low 80%s (very low) when my mask falls off.
What bothers me about these sleep tracking devices is they are often "on the low" reccomended as ways to detect sleep problems like sleep apnea. This might not be done by the companies themselves but it is certainly done by influencers who are hired to promote these products. If someone were to buy an Oura ring because they snore (one of their marketing tactics) to try and see if they have sleep apnea there is a high chance that the app would tell them their oxygen levels are fine and then they'd never go get a sleep study (which cost less than an Oura ring with home kits now). Assuming this caused them to never follow up on that snoring again, Oura's (and other companies) marketing and mediocre tech would quite literally shaved years off this persons life.
When I asked my doc if sleep apnea could kill me if left untreated, he responded, "It WILL kill you if we leave it untreated."
[0]: https://www.youtube.com/watch?v=niLuR68YleI 2min41sec