I have just exposed my first roll of Retro 100 Tonal @ ISO 100 and developed in rodinal 1+25 for 9 minutes at 20°C.
In my opinion, grain is not very thin, but it is very well defined, and tonality is beautiful.
I think that we do not have to compare it with APX but with Acros 100. I'll do the test further. And I'll test other developers too.