BUGS
Multiple checkout in general is still experimental, and
the support for submodules is incomplete. It is NOT
recommended to make multiple checkouts of a superproject.
It complicates git with more cruft. A separate clone is more understandable and independent. If you trash something in its .git/ subdirectory, only that repo is affected.
I'd hardly call it "cruft". Git has a lot of features. Not all of them are useful for all combinations of projects, workflows, and people.
In my use case, independence would be an anti-feature. git-worktree fulfills a specific desire that I cannot fulfill with any known alternative. Therefore I use it.
As for actual bugs, I certainly never encountered any. But I also don't use it with repos that contain submodules, as per the warning.
It complicates git with more cruft. A separate clone is more understandable and independent. If you trash something in its .git/ subdirectory, only that repo is affected.