Well for us we have not really had this issue. We did have one couple that we met, that we did end up giving them a FMF encounter as a b'day gift to the husband. This had been discussed by MrsVan, myself and the other wife in detail before it happened. It was a suprise for the husband.
Now if anyone has taken one for the team it was me.
It was one of our first encounters and well, it won't happen again.
For us, we both enjoy watching the other be pleased and so in that regards, if it was discussed ahead of time, we would have no issues with either a MFM or FMF encounter with other couples.
-Van