I lived in the US for a few years and my experience of these toilets is
that the narrow "throat" (what a disgusing throught) required for the
syphon also leads to many blockages. I lived there for 4 years and had
3 blockages in my toilet and heard from many others who had the same
problem.

The "flap valve" system in the cystern seems like a very good idea as
it's extremely simple. However, they are prone to slow leaks where
limescale builds up on the flap and face. Also I've seen one where the
incoming water tended to lift the flap, causing it to stick in the up
position. I could only remedy this by turning the water pressure right
down.

Personally I think the UK ones are better. And I don't want to talk
about the German "crap on a shelf" things!