I've been using the Oura Ring for about two months. I've found that it has reliably indicated poor deep sleep whenever I'd sleep with my girlfriend. However, I've also seen it and (blogged about it) detect me in light sleep when I was on the phone late at night.
As for activity tracking, it's still a bulky ring, and it makes certain activities difficult (lifting, for example). I swam with it, but I'd take it off for any barbell work. Also, tech support told me that activity tracking plays only a very small role in the app's calculations.
From personal experience, readiness did not always correlate with actual performance in the gym.
Final note: The skin under the ring tends to "marinate" if you keep it on for more than several hours. As a sleep monitor, it can provide good insights. I wouldn't use it as an activity monitor.
Bottom Line: Yes, I would recommend this to a friend
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