How good is the Oura ring tracker?

Its a nice looking device, seems to work well but at £300+ its a high price.

I do find the back story interesting however, especially since its been floating around the Quantified Self community for quite some time.

My usual worries about data-portability, app access (the android app looks like it needs work), etc all come into play but as a replacement for myband2 and sleep tracking on my pebble smart watch. It does interest me.

I don’t usually wear rings but I did obviously have a wedding ring and also did try wearing one of those cheap NFC rings.