Tonight's testing was interesting. The attached shot is a single 60s exposure, flat calibrated, no dark, stretched. You can find a higher resolution version here:
http://img.regolith.net/astro/ngc3372.jpg
This was taken with the Borg flattener on the Megrez 90. You can see that it is nice and flat, with no evidence of coma or astigmatism.
Unfortunately my testing of the WO FF III was rushed by some clouds so I didn't really get usable data, but oddly it seems that the astigmatism can be worked around if you get critical focus, as I did one test shot with the WO that didn't have astigmatism. I'll have to test this out again later, especially on some brighter targets. The area of sky I was using when testing the WO was lacking in sufficient bright stars to really abuse it.
Eric