Looking for a fish eye lens for my Nex 6

I don't have the lens, but IMO, it actually does serve its purpose, especially with these adapters. If I were to get one, I would surely get it with it the UW adapter (I already have Rokinon 8mm Fisheye).

I think the lens gets maligned primarily for not being sharp in the corners wide open. IMO, at this focal length, I wouldn't use the lens primarily wide open anyway (unless low light demands it, in which case, chances are, the corners won't matter).