IMO Flutter similarly to Apache Cordova is all or nothing in terms of UI.
If you plan to write your app solely in Dart/Flutter then you’re probably perfectly fine. But can you really tell in advance, you won’t ever need to rewrite some performance critical parts of your app in native language?
With Flutter, you are forced to make this decision early as your app needs to written solely in Dart and Flutter. The reason is Flutter’s widgets. They are not native widgets, but rather just imitation. In reality all Flutter widgets has to be rewritten from scratch. But there always will be some visual differences between Flutter and native widgets. Mixing them in single application will end up in inconsistent look. And your users will notice.
For that reason I personally prefer react-native or native script. Both allow you to write some parts of applications in native language and some parts in js. But look will be consistent, because both are just wrappers over native components.
However the good thing about Dart is that it’s compiled to machine code, which in theory makes it faster then react-native js bridge. But downside is, you need to learn new language, which you really can’t use somewhere else. (yes I know you can transpile to js, but who is really doing it?)