Another design choice that facilitates quick UI iteration is React Native's flexbox and styling abstraction, modeled after a carefully chosen subset of CSS features. Layout tweaking using the flexbox model rarely gives me any unpleasant surprises, unlike my traumatic experience grappling with Interface Builder's constraint editor.
React Native borrows the virtual DOM diff idea from React and makes it conceptually simple to write high-performance UI. If you try to repaint a full-screen background 60 times per second, RN will stutter; but for most non-game apps with few moving parts, it's not hard to create a smooth experience.
Facebook finally unveiled React Native for Android yesterday, almost six months after the iOS release. However, porting my RN app to Android is non-trivial. First of all, some of the UI controls such as SwitchIOS need to be replaced with Android counterparts; some (e.g. ActionSheetIOS) must be scratched and redesigned for the targeting platform. A more pressing issue is porting all of the native libraries my app depends on. I'll end up writing Java extensions or waiting for others to do it.
There's also no obvious way to write Apple Watch apps in RN yet.
React Native has fewer than 30 built-in components so far, iOS and Android combined. Chances are good that you'll need to find (or write your own) extensions to implement some basic features, for example, accessing SQLite databases or supporting in-app-purchase items. You'll be hurled back to the Dark Ages of app development, so be prepared with some knowledge of Objective-C and Java. Fluency in native code will be useful anyway even if you don't write RN extensions because: (1) React Native's documentation isn't on par with Apple's yet. You'll sometimes need to dive into the .m files to ferret out implementation details. (2) React Native is still a young framework, fraught with bugs on the other side across the JS bridge.
ES6 language support
Although you can use ECMAScript 6 features in your RN app, be aware that when you run
for (... of ...),
yield, etc. This is not technically a RN issue, but it will bite you during the release phase if you go too fancy with ES6 goodies.