Meters need different calibration with pyro negatives because the paper sees stain as pure density, while the meter (any meter) sees stain as not much of anything at all. Interestingly, the spectral absorption of pyro stain resembles nothing so much as an OC filter.
Some developer/film/process combinations produce a yellow-green stain - if this is seen as 'color' by VC paper, and thus effects paper contrast, I would recommend staying well away from any attempt at using a meter: it will waste your time and annoy the meter.
The real problem with metering pyro is that the stain density isn't always proportional to silver density.
However, in some serendipitous combinations the silver density and stain density follow each other quite well. Under these conditions calibration is easy, and any meter will work.
For the rest of the combinations, though, the ratio of stain to silver changes with negative density. It is possible to calibrate this out by having the meter's internal calibration change with changing negative density, and this is what the DA meter does. The instruction manual on the DA web site
http://www.darkroomautomation.com/support/pempyromanual.pdf (starting on page 7) gives detailed instructions on determining the needed adjustments. If it turns out that stain=silver in your process then you will have no trouble with any meter.
It is very important when attempting to meter pyro to maintain the same developing procedure for all your negatives. The silver-stain relationship seems to be influenced by changes in agitation. This is probably due to the way pyro quickly oxidizes and thus the activity of the staining developing agent declines in proportion to the activity of the second non-staining agent over the course of development. As development proceeds the density in the highlights (dense negative) builds more quickly in proportion to the density in the shadows (clear negative). As a result the ratio of stain to silver is different in the highlights and shadows.
Developers that oxidize more slowly will give more consistent results - PMK and PyroCat are two good choices.
You can run into cases where calibration works one time and doesn't another because the way the stain to silver ratio changes with agitation or developer age (with ABC minutes count).
You can also run into cases where one side of a bit of sheet film works fine, or the outside spiral of tank developed film works, but the rest of the sheet or roll doesn't meter properly. The reason is that the agitation of a sheet of film in a Jobo tank isn't consistent over the sheet, nor is it between the inside and outside turns of a reel. Try it - fog a sheet to ZV, develop it in pyro, bleach all the silver out and see if the stain is consistent across the sheet.
In my first investigations with metering pyro I just happened upon one of those happy combinations where the proportion of stain to silver is copacetic - and said to myself "This will be easy." Then I tried different combinations, just to make sure, and suddenly things went quite haywire. It took quite a bit of investigation to find out just what was going on.
I would approach metering pyro as an interesting exercise through which you will learn a lot about pyro and your technique. I wouldn't recommend metering as a way to increase darkroom productivity. If you want to increase productivity and decrease waste stick to D-76 1-shot diluted 1:1; then a good meter (there are only two: DA & RH) will work wonders.
