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. Or look at Ed Ting's site for his review of Parks (4 star rating I seem to recall). 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.