I know of two homes that have the Aquia in their main baths.
The Trapway is 2-5/8"
One of them mine, and one Cathy's.
Cathy's kids love the Aquia.
It's just a normal toilet that looks nice and flushes quickly.
It gets more use that the other toilets in the home.
I've been installing dual flush toilets since 98, and the Aquia is the nicest one out there right now.
I think I've sold about 60 since they came out in the US.
They've been in Tailand for six years.
Dual flush bowls do hold less water, though the trap seal remains intact like any other toilet. No difference there. The room should smell clean between uses.
Less water though, so I would say just a bit more attention with a brush for cleaning sometimes.
The bowl rinse does cover the entire bowl well.
I've been using Clorox with Teflon bowl cleaner, and that has been keeping things pretty clean.
There are some 1.6 bowls that don't stay this clean.
The Kohler Cimarron misses the bowl wash in back. The Titan is pretty slim on bowl wash. The Vortens 1.0 bowl with Flushmate needs lots of cleaning.