Matthew Walker, probably the best known sleep scientist, has been critical of Oura and pretty much all the sleep trackers for sleep phase data. Unsurprisingly,

Matthew Walker, probably the best known sleep scientist, has been critical of Oura and pretty much all the sleep trackers for sleep phase data. Unsurprisingly, it's difficult to guess at brain EM wave patterns from a band on the finger, wrist, etc. I'm 6 months on Oura, and I don't think it's actually that consistent, i.e. I don't think you can say "Oura shows 50% more deep sleep today, so even if the base mumber is wrong, I must have gotten 50% more deep sleep". I wear a fitbit to cross validate each night, and the readings on both often contradict each other seemingly arbitrarily, night to night. Overall I've found they're great for tracking overall sleep time (HRV, heart rate, temp too) but I don't read too much into the actual sleep phase data. (Day-to-day self asessment of cognitive performance is probably the best proxy.)