How’s the browser experience?

It’s pretty good TBH, I don’t miss much from Android on this front in terms of functionality.

I’m using KDE’s Angelfish (which is webkit-based), since I couldn’t find anything firefox-based with a good mobile-friendly UI. It has adblocking, page translation and forced dark mode, which is enough for me to get by. There are also some neat features like PWA support (which I use for my public transit app), and I don’t remember the other ones right now but they’re there.

Also, are there any features/tweaks you are aware of that you could not get through Nix, that the more “commercial” Linux device manufacturers have developed for their devices?

That I don’t know. Maybe some of the paper cuts could be solved on other platforms, but AFAIK 3/4 main gripes (call audio, map app, battery life) are issues on every Linux phone.