I believe OURA is living on borrowed time and only exists because Apple hasn't yet entered the smart ring market. It's a repeat of the Fitbit situation. Before the Apple Watch launched in 2015, Fitbit had 30% of the wearables market. Then the Apple came in, and Fitbit started bleeding users: high end ones to the Apple Watch, and low end ones to cheap Chinese competition. Fitbit eventually collapsed and got sold in a fire sale to Google.

Apple is already rumored to be working on their own smart ring. Samsung is already in the market. This is one reason why Oura is in a rush to IPO, they need liquidity for early investors + cash to compete before Apple comes in and takes a huge slice of their market.