I saw it in London; it was brilliant. Very, VERY exciting stuff. Also, some of the actors specifically learned to play their instruments for the production, while others (like the young man who played Anthony and was a conservatory-trained cellist) already had the expertise.
I'm only troubled by the idea of transferring this intimate production into a big theater -- at the Whitehall in London, the small space made the performance very immediate; I was in the front row, which was on the stage level, and the action was happening about 7 feet straight in front of me.
I *do* hope it succeeds on Bway, though. It's one of the best Sweeney's I've seen.
"Sweet summer evenings, hot wine and bread /
Sharing your supper, sharing your bed /
Simple joys have a simple voice:
It says why not go ahead?"