I have an excellent Parks Optical diagonal for sale. I bought a TeleVue Everbrite and have been using both trying to determine the difference. The TV is supposed to be 4 or 5% more reflective, but for the life of me I can't in all honesty say I truly see the difference. At times I think I do, but wonder if it's just suggestion. In any case I reasoned that I have all these $300 eyepieces and should have an expensive diagonal too. So the one I've finally decided to sell is the Parks Optical.
If you want specs on it, go to scopecity. I bought it new about a year ago. and am only asking $89 shipped for it. It comes as an SCT 2" thread, but I can substitute a refractor type thread I had machined for it instead, or you can have both for an extra $10 bucks, or just specify which you want.