Not personally, but I know a couple of people who have/had it, and it was generally regarded as a decent product for the money. Nowhere close to the league of the Nikon equivalent, but acceptable for the price, and surprisingly well made as well. Of course it's a fully manual lens, and if you were to shoot towards the sun, or other strong light source, I suspect that the flaring/ghosting would be significant... I believe it also suffers from bad CA, but that's generally controllable in software.
You're talking fish-eye right? I've used the Opteka 6.5mm which is $100 less but seems more or less the same lens. It works very well for what it is, though it does suffer from the flaring the tirediron brought up.