The Stunt, Stunt 9, and S9 are all terms for the same model boat. I sailed one at Foil Week in Newport in early September and enjoyed it. I sailed in marginal foiling conditions (maybe 8 mph) and was told when we got to shore that it would be priced at $22K in the U.S. (boat, originating country tax, trailer, and delivery to U.S.) I looked at Mark Batchelor's Exploder A Class cat and learned from him that they are available for $25K. I would spend the extra $3k for that boat over the S9 if I was in the market for a foiling cat. I would also wait to see how the production UFO turns out as all they had at that time was the prototype and were anticipating selling it for $9K and that would be way easier to transport, rig, launch, retrieve, store, and pay for if you just wanted to go foiling.