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regards.

It was well known for giving fine grain in the negatives of the day
(1930s? 1940s?), probably because of its solvent action on the silver
grains. Of course there would be an acutance penalty for that (might as
well use D-25?) that probably did not matter as much with 4x5" and 120
size film as it would with 35mm. Also, there tended to be about a 2-stop
speed loss.

Since these days you can buy pretty fine grain film, and with small
negatives you need (for most images) all the acutance you can get, you may
not want to deal with paraphenylenediamine anyway or any solvent develper
for that matter.

It also has a reputation for being carcinogenic. Derivatives are used in
color developers, but they are typically loaded with long hydrocarbon
chains to make them less soluble in in things such as human skin. Even if
they are not carcinogenic, they are irritating.

The reputation that Metol has for being allergenic is mostly (not
entirely) due to ppd impurities in it as a result of the early
manufacturing process. Ppd does not seem to be a common impurity in it
these days. But people can be found who are allergic or sensitive to just
about anything.