Thanks for the feedback on the animations. I didn't want to keep too large of a .gif in the repo but that's the only format that's straightforward enough to have displayed inline so I had to keep the animation terse (and admittedly a bit too fast).
It is indeed using fzf in a specialized way so that it only searches for git worktrees and nothing more. The use case I have is that I have dozens or hundreds of repos in various locations on disk and this tool makes it easy to instantly jump into any of them.
That's why it's called "gcd" -- git + cd.