I've tried to use it to mirror an old Hg repo in git, but ran into some really weird errors with branches in Hg causing vague errors. I couldn't get any help on the mailing list, and I ended up giving up right as the project said "Forget it, let's just move to Git."

This was about six months ago. I don't have the error message. I got the impression that the documentation and the support were pretty sparse for this plugin. Though, it may work well for more simple Hg repositories, I guess.

Yes, it works great. If you prefer hg you can push your code to github and get pull requests, etc. from people who only know git.

hg-git works flawlessly as long as you are using hg-git _and_ python-dulwich from their repos heads. Their releases on PyPI are always somehow out of date.