I have an O2, I got it to understand my recovery better and in particular sleep. I was aware that sleep levels would probably not be too accurate but I had no objective data other than I didn’t think I slept enough. Overall I have been pretty impressed, it has given me some useful insights and picked up when I got a temperature and felt rubbish (not COVID). The Readiness score is just an indicator for me I look at it but go much more with how I feel. It does seem to be reasonably consistent.
Downsides are it does not synch with TrainingPeaks (least not that I have found) so I sometimes forget to add an activity to the Oura app. The O3 will overcome that issue.
I did not go with Whoop because I did not want a watch like device and the subscription costs seemed too much.
I am seriously thinking about the upgrade to a O3.