> Animation in React Native is much more of a hassle than UIKit or even CSS. (About the same as native Android, though, where it's also pretty tedious.)

My experience was that RN was way more helpful on Android than on iOS, in general. But that has more to do with Android than RN, which achieves its utility on that platform by papering over a pile of bad decisions, inexplicable awkwardness, and half-finished-apparently-by-the-Summer-interns APIs, none of which should be problems in the first place. I'd seriously consider using it for just for Android even if I wrote a separate, native iOS version of the same app.