When Windy City had the ARM tower on their show, it was grossing just as much as some of their kiddie rides. At times, I think their mini Mosser Tower beat it. I want to say when they first got it they charged (or tried to at least) 4 or 5 tickets and when they sold it two years later they had dropped it to 3 tickets ($1/ticket).
Freddy Miller bought their tower a few years ago and loves it. I really think it depends on the show, the route, and what you expect as far as results.
I have talked to owners of Mega Drops (Frank Z, Tommy Thebault, Mary Talley, Jim Drew) and they all have said that their Fabbri version makes a lot more then the smaller ARM model. Jim Drew told me that it does well, you just have to know how to run it to get the crowds moved through.