I'm interested to try flutter out on chromeos, I might get a chromebox, the acer and hp i5 U series are the recommended ones for Android development. Developing flutter without the need for a simulator or a phone connected via usb, is cool. Maybe the next step is develope android flutter apps on android.

With regards PWAs, maybe more so on mobile, flutter apps are AOT, Ahead Of Time, compiled for release so they should have better start up times than apps that run on a vm.

The flutter wiki has stuff on the diffent modes. https://github.com/flutter/flutter/wiki/Flutter%27s-modes

Debug mode "Optimizes for fast develop/run cycles." runs on the Dart VM and allows for statefull hot reload.