Well since you ask: Flutter is good, but it's also buggy.
1. Problem with Cupertino theme on Android - https://github.com/flutter/flutter/issues/42988#issuecomment... -- only point 1 from this post matters, because point 2 was resolved by a helpful person below the post. But point 1 is still unresolved, and it looks bad.
2. Flutter runtime simply crashes on some mobile phones when loading the app. I've released an app on old SDK, and with every update of some minor thing + SDK I'm getting reports about new crashes from people who rated the app 5 starts on older SDKs, because it was working for them earlier. I've tried to report it: https://github.com/flutter/flutter/issues/43240 but my issue was grouped with some unrelated problem, and my questions were ignored.
3. I think the x86 codegen in Flutter is sometimes buggy. I've used a ZIP compressor/decompressor library written in pure Dart and it sometimes crashed in random location after using the library. I've tried to debug it but there was no pattern for the crash. The crash also was happening on the system level (SIGSEGV) instead of simply throwing an exception that would be catchable by Dart. When testing on the mobile phone, so when ARM codegen was used, I've observed no crashes and no problems when using the archive library.
4. Google AdMob has poor support for Flutter. The official AdMob lib doesn't support native ads, and is incompatible with widgets that draw an always-on-top layer, like Drawers or Action Buttons at the bottom right corner of the screen. It IS possible to finally work out the solution by using some thirdparty library which uses AdMob in a hacky way, but I would expect something better for one of the most crucial Google services like AdMob.
5. Until recently there was no support of Cupertino theme's i18n. I had to manually translate all texts of Cupertino theme to a different language (like 'copy', 'paste', etc).
I've released two apps in Flutter but I'm afraid to update them, because something always breaks after update.
I worked on a react native project a year ago and hated it, mostly because of the story regarding interop with native code or SDKs. I imagine my experience would have been a lot better if the team didn’t “eject” from create-react-app-native, but I’m not sure how feasible it is to develop an app with ejecting.
Then I regret looking into Nativescript, because it was pretty buggy.
Then I regret not knowing about Flutter earlier.
THEN I regret not knowing that Flutter is pretty buggy as well.
Next step is me trying to learn other frameworks, like Cordova or React Native. I wonder what my regrets will be.