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No worries, Arthur. My motto with EP's is "try before you buy".
My mirror is superb, with a Strehl ratio of 0.96 and excellent RMS, but at f/5, it shows up coma in a lot of EPs, including the Widescan, which shows particularly bad coma.
I recently borrowed a Pentax XW and a Nagler for comparison, and my opinion is that the Pentax produces better images. The Pentax design, and some of the Naglers too, have an adjustable EP design, which may help you with the image blackout problem you are describing.
At the lower end of the budgetry range, I have found the University Optics orthoscopic EP's (which retail in Australia for $125) perform very well with my fast mirror. Their only limitation is that they have a much more limited 40-45 degree FOV.
Personal preference plays an important factor too.
Good luck!
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