You can have multiple worktrees per repo. Usually that's the best solution instead of local clones.
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.
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.