I have had some duos that didn't live up to the hype, but some (and even a trio) that were great. (One for certain that was like watching a VR porn film that somehow was starring me.)
For me though, being with two ladies is only an option if the ladies are totally into doing each other (to the point where they'll have at each other without my prompting).
This leads me to my other [opposite] point:
If they are not into pleasuring each other, it is just not worth it for me. Others may feel differently, but two women alternating doing X to me, doesn't really improve the experience.
For the kind of extra money I'd spend, I'd rather be with just one lady for a longer session, or have two shorter sessions with two different ladies (and I do not mean one right after the other).
And that is the consideration. A duo costs double or more - cutting the time down just to have two women is nonsensical; if anything, more participants should mean more time for all that multi-directional enjoyment. That means the cost bump will be huge. You have to expect that just going into the idea. I sure wouldn't want to pay double to still have to rush my ass out the door.
Maybe this is just me though - I am not a fan of short sessions to begin with. The only times I've done less than an hour with any SP were when I booked an hour, but got disappointed and left early.
In any case, yes they can be very fun, but don't go in with some bargain basement expectations. It is a special treat, so consider paying what it takes to make it special. If that means it's also a rare treat, so be it.