In the city, there were a few places that would offer packages where 1-girl would give you a TS and then start your massage for the first 20 minutes or so. Then the second would join in for the fun part for another 20-30 minutes, and then the first girl would leave and let the last girl wrap up the session. I want to say that there were different time spans offered, like 1hr, 90-min, 2hr.
I never went to any of these spots, but found them interesting.
To answer your question. 4-hand at an AMP is somewhat of a let down, at least in my experience. These girls typically want nothing to do with one another, so it's somewhat mechanical. One girl tunes the engine while the other one holds the flashlight, and cleans the windows.
However, if you get 2 girls that enjoy playing with each other just as much as you, then you take that white Buffalo, and ride it until the cows come home.