Yes, had experience of one on a Westerley about 10 years ago, it was ok-ish, never really brilliant, tended to break the vertical lines now and then but was on a charter boat I looked after so it probably got a harder time than most.
IMHO better off with lazy jacks and a sail cover fitted to the boom with a zip running alon the top.
I've had one and it works well, particularly with a fully battened main. But it is quite expensive and you must also modify your sail cover - overall, probably more expensive than a stack pack type system with lazyjacks I think.
