OnePlus opted for RTOS instead of Google's Wear OS and against an always-on display due to battery life concerns. However, that and an equivalent to the Play Store's Health app for the iPhone are reportedly already under discussion. We also found a few software bugs for the developers, but we are otherwise excited about the smartwatch. And not only because of its low price.
https://www.notebookcheck.net/OnePlus-Watch-in-review-There-are-still-some-teething-problems.532699.0.html