I can not comment on this in regards to real life expierence but i do have a few thoughts for you to ponder.

How will you feel after it happens, does everyone just go on their way or spend the night? How does it end

What if you or your partner say something while excited and playing that the other person is upset by eg, that feels so good or something they feel should not have been shared.

DO either of you ever, ever toss out jealous comments about things that happened that upset one of you during a fight. In other words is it a possibility the fact the encounter was enjoyed become ammo in an argument.

If its people that you know socially how will it be to meet again. Is there concern about one of the parties becoming too close to one of you.

How open have your communications been in the past? This needs the biggest amount of honesty ever, good or bad it has to be able to be talked about.

Will you become ashamed due to guilt about it later (only you know how you feel about your sexuality) Does your partner read your underlying feelings well enough to understand it.

Try to imagine the encounter from start to finish and allow yourself to feel what the reality may be as opposed to the fantasy of what happens. think about it from start to finish and then what may happen when you are alone again.

On a side note I wonder how on starts out these things haha I can never quite get over how it would start in real life for me, but that is just me.

Have you considered the location, if its strangers to you can you trust them in your home , if you have children you may not want it to happen in your house Your safety on dealing with an unknown couple must be also considered.

If its a friend then what if you and your partner are fine with it later but they are not and get all weird on you. Are you willing to perhaps loose a friend that can not handle the reality?

I do think it can work but it means a very hard look at all the ramifications as you are trying to do in this thread. Good Luck