The Aquia didn't have great flushing reviews if I recall, or it isn't skirted, so is ugly at the bottom, and I like the sleek low profile.
If you can't figure out what the "big consumer retail site" is... Oh well.
In any event, you found the parts so yay.
But talk about not having done your research.
Two piece Aquia clearly not skirted (rolling eyes):
Nor is the one-piece Aquia (again rolling eyes):
As to the reviews saying it doesn't flush well, I don't know where you are looking, because Terry consistently says that he installs a lot of them (I mean thousands, literally) and that customers don't return them, they call and order more of them. And the reviews at places you should/would find believable also laud the Aquias. Not so much for the Inax stuff. But, hey, you like the way the failed St Clair looks. So go for it.
One other toilet that looks a bit like the St Clair but isn't a dual flush, and works well, as Terry says, the Toto Legato: