I've heard directly from some cat sailors that have tried them and they say that they're extremely unstable until you get it airborne on the foils - at that point, they're solid as a rock (which makes sense since the foils have so much more beam than the boat itself).
I suspect the increase in stability when foiling has a lot to do with the increase and steadying of the aparant wind that results from being on the foils. We see the same thing when windsurfing with modern (planing) light wind equipment. Once the board pops up on plane everything steadies out and the apparant wind direction doesn't vary much even with changes in true windspeed, direction, or course.
I agree, sailing one of these boats on a small, shallow, or weedy body of water would probably not be a good idea.
As for sailing these boats in 25 to 30 knot conditions, that's at or approaching survival conditions for many small boats and certainly outside of the design conditions for Moths.
Definitly extremely cool boats though for sure.
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