Hi John,
Yep, I have the mpcc and it works really well on my 8 and 10inch F4's
This was taken with a mark2 mpcc at 58mm distance which is not the correct spacing, but it has still corrected it across
Minor elongation is more due to other issues not coma
http://www.astrobin.com/full/24613/?mod=none
I just sold the mark2 and got the mark3 as it has 44mm aperture compared to 38mm of the mark2
Would definitely recommend it for imaging
As for guiding without a cc, I have done a 20min sub with a TS oag, lodestar and a 10inch F4 without a cc, and it came out perfect, although the stars in the guidecam were eagles, not seagulls due to the coma of the F4 without the cc. So using one would only aid not deter as the oag uses the edge of the field where coma is more pronounced.
most guiding software would work fine even if they're not round as they measure the pixel values of a certain area to get the centroid.
Cheers