I got this ring on 3 April 2020. It focusses on baseline and trending of overall health measured during sleep (a controlled environment without external stimuli). It uses infrared light to penetrate deeper than green light on most wrist activity trackers, and will there also report on temperature as well as heart rate variations.
It's claim to fame is not "live exercise" tracking as it has no display and does not actually give any summary of specific exercises like the Fitbiot and similar trackers give. It is literally the size of a normal ring so for those who do not like wearing wrist trackers and are more interested in their overall health (or illness) then the Oura Ring could be a good bet. It is about the price of an Apple watch but this ring does work with Android phones, which the Apple watch does not. There is also a case made for its measurement on the underside of the finger being more accurate than from the top of a wrist (hospitals connect heart rate sensors to the finger too). More about its sensors at https://ouraring.com/get-to-know-oura. Some validation studies can also been seen at https://ouraring.com/oura-validation-psg.
UCSF Health and Oura are teaming up to study whether Oura can provide signals that predict COVID-19 illness symptoms. Oura is inviting all users to join the study.
The photos in this album will be documenting what I'm observing about the ring, and also how it compares to my Fitbit Charge 2.
UPDATE 9 Apr 2020: I have been monitoring the first week's battery life and these are my observations: On the 6th calendar day at lunch time Wed 8th April (started lunch time Fri 3rd April) after 5 days of actual usage, the battery warning came on at 25% remaining capacity. This indicates about 15% used per 24 hours. About 11 hours later at 24:00 Wed bedtime it had dropped to 24%. Next morning at 9am Thurs 9th it was at 9% so it does use more at night while in sleep mode. By 13:07 it was down to 7% when I put it on charge. It was fully charged after one hour and 31 minutes. For exercise monitoring I attempted to run a 30 minute "Body Status" check but it reported problems from excessive hand movement so is intended for meditation and no-movement checking really.
UPDATE 22 April 2020: A video on the weekly report that comes through the mobile app - see https://youtu.be/YgZ9hGBF8-M.
UPDATE 3 May 2020: A video on how the correlation trend data works at https://youtu.be/Fmm0Ipsb3Ao.