Just a comment on Ed Buffaloe's message in which he stated that the only failing (of Pyrocat-HD) is that it does not have good keeping qualities compared to PMK.
Ed is correct but the comment must be taken in perspective. As we know, the keeping quality of PMK concentrate sotck solutions is about as good as it gets. Several years ago I mixed a working dilution of PMK from stock concentrates that were over two years old, and the results were as good as one would expect form freshly mixed stock.
On the other hand the keeping quality of Pyrocat-HD, which is on the order of up to six months in partially full bottles, is really quite good when compared to other developers. I would never, for example, trust 6 month old D76 or Xtol but I have developed quite a lot of negatives mixed from Pyrocate-HD stock concentrates that were 4-6 months old.
Some people have substituted metol for phenidone (at about 10X the amount of phenidone) in the Pyrocat-HD formula and in theory this should provide even greater stqbility. However, although my original Pyrocat formula contained metol rather than phenidone, I don't recommend the substitution at this time as the phenidone version gives slightly greater effective film speed and also slightly lower b+f.