Usually size is never an issue for me but I have to admit that size DOES matter on this one just a bit, but it can be a wonderful feeling if both the guys are not really really big!!!
I've been a part of both FMF and MFM, but never a DP. From what I do know, from Adult Industry friends, it actually takes a little coordination between the guys to make it really good for the F involved. lol I know some girls that absolutely LOVE it, I just havent been around when they wanted it. LOL