The lens is actually well made, and focuses very smoothly. As it turned out, I was surprised that it's quite decent. Maybe not as good as the Minolta Rokkor 250mm f5.6, but it certainly is not a dud. In terms of sharpness, it's passable for a mirror lens, if you can focus it properly. You may notice that all the pictures below are kinda grainy, that's because I had to set the shutter speed to around 1/1000s to maintain safe shutter speed. At that kind of shutter speed, even in broad daylight, the ISO is around 1600. This is one reason I don't like mirror lenses. The 500mm focal length (750mm equivalent on NEX-6) is way too long for most purposes. Holding it to my eyes, I feel like suffering from ET; the view jitters so badly that focusing becomes a problem. Seriously, I don't know what good a lens like this is for. It's too slow for action shots/birds, too long for most uses, and putting it on a tripod is almost mandatory. The only positive I see is the very light weight for the focal length.
I shot quite a few pictures, but the keeper rate is rather low, due to blur. I am sure if used on tripod, it will perform much better, but I am not a tripod guy. Maybe a camera body, like the E-M1 or E-M5, with in-body-stabilization, will make it easier to use.
All pictures below were shot using a NEX-6 & Quantaray 500mm f8 mirror lens. Except for the third picture, all were taken through very thick glass from 17th floor.