Possibly for the "extra deep" requirement, but consider the aesthetics. Plumbers don't think too much about the overflow and drain trim matching the fixtures, but you certainly will. I had one client that didn't like the price of the drain so her plumber used a Gerber. Sure, it's brass (not plastic), but it didn't match her new tub/shower at all. She was not happy.

Given some of what I have read elsewhere about the Tea for Two tub, your plumber is probably wise to install a different drain than the "mandatory" Kohler drain, which is almost universally detested by owners of this tub for its failure to function correctly. I'd be interested to know what type of drain your plumber plans to install as I absolutely love the Tea for Two tub, but don't want to have the drain problems that so many owners of this tub have. Check out the reviews at Amazon.

Here is a link that might be useful: Kohler Tea for Two Reviews on Amazon

We installed 5 of the T42 tubs in our project, against professional advice, and it turns out the pros really knew their stuff-
After a month the first drain failed, and after three years the only one still functioning is the one in the guest bath.
That
one still works (and we're only guessing it still works, we haven't
dared actually try it) because no one has used the tub for a bath, only
showers.
Take it from one foolish enough not to listen, if you're thinking of using Kohler: think again.
If you go ahead and buy, don't blame Kohler (and they could care less) blame yourself.
Ha!