Great when it works (in general) but a bummer when it doesn't and you need it most (like while reefing).
Had it on charters a couple of times and worked fine in light (below 10 knots) winds but was more difficult to use at around 25 knots.
The real bummer was when we needed to reef (I am always too late to admit that you have to) and the car flew from the boom showering us in ball bearing parts. Whish I had the normal idiot proof slap reefing system there and then.
Other than that the sail shape is never as good as with normal sails. Even with vertical battens (have you ever had to handle those 60 Ft!! pieces of glasfibre) I was dissapointed.