Relayer, what old time formula is that?
Michael Gudzinowicz was a good contributor to the old Google groups.
IMO P-aminophenol has 2 advantages over metol at high pH:
(1) It does not hydrolyze (react with water), see my 62 year old Azol test:
(2) Homebrewers can make it from Tylenol/Paracetamol capsules or caplets, as in PaRodinal.
Metol has 2 advantages over p-aminophenol at lower pH where it is stable:
(3) It is sharper.I find acutance in the order FX-1>FX-2>Rodinal=Pyrocat.
(4) It develops in half the time.I found a D-76d copy made using PAP instead of metol produced similar grain but took about twice as long.
The structure of Metol and p-aminophenol in solution where they are ionized is similar but Metol has a CH3 group instead of an H group.
It's possible that this may mean that the Metol is more ionized and reactive but I have not read any comment on this.