I recommend react-native-config for its ability to expose config variables to native code. For instance, when building an iOS RN app, the JS Bundle is handled differently for production apps vs development. The build type variable needs to be available in AppDeledate.m (in the RN sample) so that the initWithBundleURL parameter is set up properly.
This may not seem necessary until you build for production release. Save yourself the refactor pain and stick with react-native-config.