I love the look of built-in flush.
However, entry to the tub seems like it would be awkward to me.
I think a height where you could sit on the edge of the tub and swing your legs in for entry makes sense.
My local repair guy told me that customers will too often build it in without leaving room for entrance for service.
So, semi-sunken with good clearance for service makes sense to me.
It _will_ have to be worked on, probably more than once. Give it ten or fifteen years and you are talking several times at least.
Service bills may be a lot higher than you expect if there is not ready access.