I've been using mingle for about two years now. It's easy to set up, and easy to use. I don't think it's being seriously supported much any more, though I do occasionally get an update.
My only complaint is the comment windows. Users don't have a Preview, and they can't easily make they're comments look nicer with HTML buttons. IS this because of security that html is not included?
Anyway, it is a great plugin if you want forums. I've not had anything break. I did have a conflict with Jetpack, and had to remove Jetpack and use a different stats plugin.
I do recommend Mingle, and hope the developer continues to develop it and add features.