So far so good. The flush is so quick/short that at first I thought something was wrong - but it seems to be taking everything down just fine. I did notice that if I don't hold the handle for a split second - it sometimes cuts the flush off too short. But when I watched the flapper in operation (tank lid removed) there wasn't any slack in the chain that could be taken out. So I think the flapper is designed to be sucked back into the closed position very quickly - before the tank is close to being empty. In fact, the flapper has a molded hole to keep it from trapping air - which would probably make it float up/open longer.
ALSO> I used the Fernco waxless connector (http://www.fernco.com/FTS.html) and absolutely LOVED IT!!! It adhered very tightly to the bottom of the toilet and inserted very securely into the floor pipe (I had to coat the sealing ridges with liquid soap and work the toilet down into place). Assuming it holds up (I can't imagine it wouldn't last longer than wax) - I'll never use wax again except with an offset fitting - which won't accept the Fernco fitting.
Just push the Fluidmaster onto the bottom of the toilet.
I helped a friend who tried the Fluidmaster waxless fitting earlier this week and we ended up reverting to wax because the Fluidmaster design gave us no confidence that it was seating/sealing properly to the bottom of the toilet outlet. The Fernco product - with it's thick/sticky pre-applied sealent eliminated this issue.
If you haven't tried the Fernco product - I recommend it - especially for DIYs like me - who don't have the experience/technique of a pro. By the way - I don't work for Fernco ;^)