I have the Gwyneth in my main bath.
It works fine.
And in the first floor, a Sanagloss Ultramax. That works good too.
I do clean them more than I would something from the 80's, but the 80's are long gone. It's 2009 now.
A single flush works fine with these. All solids go down with one flush. If sometimes you need extra cleaning, it's easy to hold the handle down a bit longer, or to eve flush twice with the Gwyneth, that would only be 2.56 gallons, still much less then 3.5 or 5.0