I have had the luck to have 2 separate experiences with FFM.

The first time was with my then girlfriend and her mate. It was a lot of fun at the time, but the fallout was not. I would seriously advise anyone considering it to make sure there will be no jealousy. It is all well and true setting down ground rules beforehand but alcohol and horniness can soon see those rules broken.

The second time was with 2 girls I am still friends with (but have never dated), we were drunk and it was a lot more relaxed and a lot of fun. None of us have mentioned it ever since but I would definitely do it again with 2 girls.