It depends. If you want to write nice looking material design app, then yes, it works really well. As iOS developer I can say that flutter is much more pleasant than storyboards & UIKit (which is probably why Apple is working on SwiftUI).

It's a different story if you want to use native features. Plugins provided by community offer only basic functionality, and are often very buggy: you will encounter iOS bugs, Android bugs, Flutter bugs and plugin bugs, all in one package. Anyway, it sort of works if you plugins provide stuff that you need. If they don't, you are forced to fork the plugin and add ad those features, learning Android or iOS during the process, and writing a lot of boilerplate for communication.