I agree that you won't be able to see much if anything between say a GSO mirror and a Royce mirror with a ccd but it's the mounting system that makes it so good.
What does make a big difference is the corrector used. I found the the Mk 3 MPCC very frustrating with my scope(Royce 10" f4). I changed to a type 2 Paracorr and it was instant goodness. It does slow the scope down to f4.6 but that a very good trade off for how well it performs.
https://farm3.staticflickr.com/2911/...3c71a20e_b.jpg
Corrector test by
Raymond Collecutt, on Flickr