I've done five duos. Only one had any kind of planning, the other four were on a whim, and for two of those they offered a discount to entice me. It's not something I'm really into, but I'll consider it if the right opportunity presents itself.
Three of the duos were great, two were disappointing. One of them we just ran out of time. They only had a 30 min window available which isn't enough. I did another duo with them for 1h and it was way better. The other one was with one girl I was meeting for the first time and wasn't into her, and they weren't interactive at all.
I never did the condom switching thing. Three of the duos were oral only, one they were ok using the same condom, and one I only did FS with one girl.