It certainty wasn't superior, and A&T don't imply that, I just re-read that bit again yesterday.
Acutol-S gave excellent edge effects but the grain & tonality suffered, it wasn't as good as Acutol (which is a different formula). It had poor keeping properties as a commercial product less than a year. So after Paterson stopped production Crawley published it's formula FX-15.
I used it back in the early to mid 70's and it was terrible with 35mm film, compared to Acutol.
Ian