An issue of safety really.
the rules are as follows:
1. If you see another man naked anywhere except the shower in a gym, you will be gay.
2. If you even accidentally touch the genitals of another man you will become gay.Assuming you are not a urologist.
That being said if you kept your eyes closed and boundaries were clearly defined and his penis was no bigger than yours it might work
My ex SO and I did the MFM thing many times and really enjoyed it! Of course it was with a good friend, so we were all very comfortable with it! And definitely no sword fighting going on.......it was all about me!
I have done the mfm only once and we were both straight guys, so as long as it is understood up front that it is all about the girl and the guys are compatable meaning both are about the teamwork involved in pleasing her it was and can be the best. I can see if there is not this compatablity and selflessness it could be not as much fun. My only issue is that I would not feel comfortable without both guys using condoms. I know with some girls it is important that the guys cum inside, and I would not enjoy that even if the obvious concerns that exist today weren't an issue.
Pulling off a MFM in the hobby is a pain in the a** i can say that..and not in a good way..
not so hard if its 2 hobbyiest that are friends in the hobby..but try to put 2 hobbyiest together that both want a mfm 3 some..agree to it, etc.. its the sheer scheduling of it all that is difficult.. conflicting schedules are a pain to deal with and hard to overcome..
however.. mfm are a blast.. done some in the hobby and outside the hobby..if the guys are comfortable and confident..its a blast
I haven't done it yet, but providing the circumstances were right I certainly could see it being fun. And yes, I don't think I would want to be outdone (too much) in the size department, or it might deflate the "ego" a little further.