First off, I'm a huge
fan of OEG-type sights and use them on all my pumps.
I prefer them over battery-powered red dots because they're essentially paintball-proof from any possible angle of impact and unlike a red dot there's no batteries to go out.
The sight in the auction is a 32 degrees "Magnum" OEG sight.
As others have said, it's a clone of the original DYE iZon which in turn was a clone of the Armson sights.
I've owned all three, and in my experience the quality of the Magnum is much better than the DYE, at least, the old ones; the dot is clear and nice and bright and the adjustment knobs aren't as prone as the DYE's to stripping out. Neither, however, is as nice as a genuine Armson.
The real catch with these cheap 32* Magnum sights is that the mounting rail can be a bit of a pain. It's ostensibly designed for 3/8" dovetail sight rails as used to be standard on paintball guns, but the height of the mounting screws prevents it from being bolted onto any but the tallest and narrowest of Dovetail rails. The Magnum I have fit fine on my old Psychoballistics Superbolt (which I suspect it was designed for) and my Action Markers Illusion, but I was never able to get it to mount properly to my Phantom, Maverick, nor any of my Spyders. The Armson, on the other hand, uses blade-type attachment and is far more forgiving and grants a surer grip.
Good info here: Is there a Less Expensive Alternative to Armson Sights?