Maybe I don't understand how gitbutler works, but the main reason I use worktrees is actually to keep my IDE and incremental builds getting confused when I switch branches, on branches that have lots of differences. It works really well, and I can fix stuff on old versions of our app in a jiffy.
I wouldn't use gitbutler for what I use worktrees, and I wouldn't use worktrees for what I think gitbutler is aiming at.