A question for Obsession owners, or those that have done a side-by-side comparison.
A month ago I had my 2001 era Obsession 20 F/5 with OMI mirror at a star party (dark skies, with good/excellent seeing) next to 16, 18, 20, and 22 inch "premium" Dobs. Both I, and some other long-time observers concluded that my scope was clearly showing more pin-point stars and better detail on Jupiter. My scope has a history of great optical performance, and very smooth movements - while encoder accuracy is sometimes not so "super" - thanks I think to the mirror box sliding sideways in the rocker box.
However -- I had very carefully checked the positioning of the primary in its Glatter cable sling - to make sure it was moving freely and the primary and secondary cells were working properly. I also took my time with collimation - and checked it a 2nd time after it was fully dark - trying to be very precise. My conclusion was - my scope's apparent "superior performance" was more a result of good cooling and precise collimation that superior optics! Learn to collimate and insure a cool mirror first before worrying about mirror quality!
A friend who makes well-known "premium Dobs" - and will sell you one with a premium mirror or a Chinese GSO mirror (at lower price, with quicker delivery time) - told me about a year ago "The latest batch of GSO mirrors I've had come in were all pretty good!" Yes, he does star test the completed scopes, and will not sell you an optical "dog".
So -- why do I want to sell my Obsession 20???
Well, at nearly 72 now - I need to get rid of the ladder, get an easier-to-handle F/3.2 or something 20 to 22 inch -- but after this last experience with the old Obsession 20 -- I'll probably keep it for another year!
When I do sell it - a very lucky 40-something person who can handle ladders, transport heavy scopes, etc, will be getting a great scope that will perform for years!