I agree with all that has been said about the effects of overall stain. In my experience, overall stain reduces overall contrast. It acts as an increase of B+F. I have even noticed with ABC pyro that if the Bisulfite gets some age that it also imparts an overall stain. The result is the same reduction of contrast. At least with ABC I know what causes it and what I can do to prevent it. In the case of PMK, it is marketed as being something of value. In fact the advertisements that coexist with the Bergger film ads clearly show an overall stained negative. The true benefits of Pyro developers exist in the fact that the tanning is proportional to silver density. Since the low values have little negative density they should have very little in the way of tanning effect from the pyro. The tanning/stain of beneficial pyro formulations will not be immediately visable to a casual observer by just visually examining the negative.