If you think a Cassegrain or Newt will not have the odd off-axis stray reflection, sorry... no such telescope exists...
e.g. this was taken with a $40K RCOS...note the rays from a pair of bright nearby stars top and left of field.
http://www.atscope.com.au/BRO/gallery10.html
GSO have told me their latest RC's have a redesigned baffle tube. As posted elsewhere, I took this test image a short while ago.
http://www.atscope.com.au/BRO/images/GSO/gsom8.html
If you look very closely there is a dim off-axis reflection in that image.
The scope did need colimation and apart from a mild spherical error, had no other vices that I could see.
The focuser handled an SBIG STL11k with no problems.
A bright star, just off axis, may still throw some scattered light onto the focal plane. Sorry, that's the way most telescopes work.
As for the RC design, they have no off-axis coma. This is very different to field curvature which they do indeed have.
That said it is very low, and would be hard to pick with an APS sized chip.