I have friends in our club who ditched the H20 for Nacra F18, and were absolutely dumbfounded by the fact that the mast didn't sink when they tipped over. Unbelievable! Sure, they'll have to make sure the rivets are always sealed, etc., but that is amazing.
All cats that do not have some type of floatation aide at the mast tip will turtle if the conditions are right (heavy air) Yeah, your friends might be impressed that a NF18 won't turtle but I'll bet you it wasn't very windy when they did flip over. I've put my HF18 upside down several times in extreme conditions. But I find it easier to right from a turtled position. At least you can pick which side the wind will help you with instead of trying to "walk" the boat into the proper righting position.