I haven't, no. But as far as I can tell from the documentation, it looks more like an alternative to stgit (with a similar lack of history or collaboration support)?

stgit is similar in that it sits with git, but it's not the same workflow. git-spice has branches per feature that base on one-another. It's more git-like than quilt-like.

What you get is git-styled patch-series development. Branches on branches where each branch maintains history of the feature.

A git-spice workflow is compatible with GitHub style PRs where a PR depends depends on another PR.

Or pair git-spice with format-patch you can share with developers who prefer patch files. Or take patches from someone and import each patch as a branch, then let git-spice track the stack position.