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.
Since we write out our virtual branch artifacts into refs/gitbutler/X, you could actually pretty easily setup worktrees from each of them to do this type of work on. Perhaps setup a post-commit hook to update any active worktrees automatically too. Might be an interesting way to effectively work on several worktrees from a single working directory.
I wouldn't use gitbutler for what I use worktrees, and I wouldn't use worktrees for what I think gitbutler is aiming at.