I'll throw this in there since I have hired ladies and gents for myself and my husband before - just skip me if you don't feel its worthy info.
I'd say I've done this 10+ times. Sometimes with the same lady, sometimes someone I've never met, sometimes on suggestion.
Personally, I've had it go both ways. Most of the time its quite fun and worth it. I'd say 8/10 I felt it was fantastic. a couple times was just ok. None of it was ever awful or unworthy.
I found that I had better experiences when I was able to convey my expectations prior to meeting. Not a play by play or a will you won't you but more of a "I'm looking for this specifically and let me know if you can meet this" Letting her know how involved Id like her to be and a brief layout of what I was searching for etc etc. It's not cheap, you should be able to be the director somewhat if you pay the right price.
There was no trait that indicated it would be bad or good. I've had girls I know rock and girls I know think they could be lazy since we were friends. If you are unsure, just find girls that have doubles reviews or just post asking for info about two girls together. People will pop up and share the info.
Also There have been a few times when I thought doubles I was sought out for didnt go as well as they could have and felt they didn't get their money's worth. Even though I did MY part, the other girl made it difficult. ( non working girl)
I have found when guys bring girls to ME (I'm not sure if you are hiring both ladies or bringing a friend) If I talk to that girl FIRST, we are able to make the time more fun. It gets past that awkwardness a non working girl may have and lets her get to know the working girl a bit.
As for MFM 3 ways, I've done this too- I think its not worth the $ unless the girl brings a guy she knows can perform and be okay in a 3 some. It's easier to calm down one guy and get him in the mood then two guys who aren't experienced. Sure, if you and another client split the fee, it makes it more economical but I can bet its going to be less fun too
Research research research =)
RHR
Just one small p.s as a provider - Most guys that I've done doubles with are usually in awe of how awesome of a time they have had and usually are talking about mind blown. This was with the MANY doubles I've done with tons of girls so I think they are usually feeling it's pretty worth it =)