I did star test it. My comments here are based on memory of events several years ago. To the best of my recollection, my C90 produced fairly round and concentric rings inside and outside of focus, The Airy disk, as I remember was more or less overcome by the brightness of the first defraction ring which was also much brighter than those further out. Also, as I remember there weren’t a lot of rings visible, I suppose because so much energy seemed to be concentrated in the first. Overall, they were prettymuch, just outright unspectacular-passible but blah. Certainly nothing like the clean Airy disk and delicate rings of diminishing brightness falling away from center as seen in a good refractor. As I said in my prior comment, it did split ε1 and ε2 but barely; ie. each pair were hardly distinct stars with just the most minute bit of black separation, tho the difference in orientation of the two oblong pairs was easily seen. I think that it was the way that the energy was distributed in and around the Airy disk that hampered the clean separation of the stars. So there was certainly no wow factor; a passing mark at best.
Thank you for responding, I didn't know.
Your description suggests significant SA - did you do the "breakout test"? Where you measure the focuser change between the in focus to secondary shadow appearance(breakout), and compare to the the out focus breakout focuser change? If they differ, there's a measure of SA. If a 20%+ difference, it's likely not 1/4 wave.
I think you had one with an improper aspherization. It was there, but not done/tested correctly.
Also, there's the appearance of zones if as you go in/out and the brightness/gap of a ring shifts. Many CAT's have zones, usually because of lazy figuring or someone tried to "fix" a zone with a subdiameter tool (often a finger) and just split the bad zone by hitting the peak. I've seen this in refractors too, especially your favorite Towa's.
Hanging around John Dobson for a few hours decades back was worthwhile, even enduring his crazy talk about physics ...