I've had several SP duos over the years, and only 2 were truly memorable and worthwhile. The idea of a duo is a real turn-on, but in practice so much is reliant on how into it the two girls are going to be. Often, it's going through the motions, and you know there's no real passion there. Sometimes it's almost a well-rehearsed show. There needs to be some spontaneity and a real connection between the girls. Genuine girl/girl sex is incredibly erotic when there's real chemistry and lust/willingness - but If it's just going through the motions - I think I'd rather save my money. And, on about 3 occasions where I've booked a duo, the girls have had little to no interaction with each other, which kills the overall mood for me.
So these days, I don't indulge. I'm sure I will again if I find the right combination, but it's not a priority for me. I've had fun with them, but they're not necessarily the incredible experience many guys may think they are.