Guess I should edit that to "is rarely directly used in pools. . . "

My understanding is that if you add equivalent -- with respect to boron content --amounts of borax and boric acid to your pool, and then adjust to the same pH, you will end up with virtually identical borate ions in the water.

And, I probably have mentioned the possibility of using boric acid. ChemGeek might well have done so, too.

I just didn't recall anyone reporting having done so. But then, I haven't read every thread here, and I don't even remember all of those I have read.