It's certainly a solid improvement in the space of VCS UI, but beware that jj has some current limitations which might prohibit switching, especially for the git power users.

Lack of gitattributes support precludes git-crypt and git-lfs usage or anything that needs filters; line ending settings will get ignored, making Windows interop a little less smooth; etc.

Also note that auxillary tooling, such as git-annex and git-bug, becomes second class, i.e. no oplog integration and they might mess up your log with internal-use commits and heads.