Paul, my point is not to compare the GSO RC to an APO refractor. Instead I am comparing the GSO RC to a simple newtonian with a coma corrector, which can produce results just as good and at a comparable cost. But a newt with a coma corrector doesn't have the marketing jazz of an RC scope. The main reason why these scopes are popular is
because of the $10K+ brand name RC's, and because people have a perception of them being cheap, not because of the results that have been obtained.
If I want a cheap scope that will give me
good performance to the corners of a KAF-16803 chip then I'll spend US$1399 (plus eschew and shipping costs) and get a simple SCT with a built in flattener (8" Edge HD). And I know that I won't have to crop corners from the STL11K like peter did, or worry about trying to get flatteners to work to realise the potential of the design.