The "blue fringe" is the hallmark of a true fisheye design so nothing wrong with it
per se.
One is of course free to make a circular mask to remove the fringe during post processing, if deemed necessary.
Vignetting will, by the way, depend on focused distance. The image circle expands slightly towards infinity focus. Thus, one can get by with the lens at 9.5 mm setting for remote subjects with a DX camera, instead of the ~11mm "safe DX" mark on the lens barrel.
As to focusing, the close focus is 0.16m thus only leaves about 3 cm free space in front of the glass; with the hood on there is just 2 cm of working distance. Don't fall into the trap of mixing up "close focus" with "macro" -- as the focal length is short, magnification isn't that large even at the near limit unless the lens is operated at 15 mm focal length in which case one gets around 1:3. Scaring away insects is easy