Hey, now that you are here, directed by an e-bay listing (imitation is the sincerest form of flattery).
I have a few of these type of lenses available for sale. Click on my profile for my e-mail.

These are an inexpensive way to get into fisheye photos, but are not nearly as good as a real fisheye.
See my Peleng 8mm galleries for an example of an inexpensive "real fisheye"
Note pronounced curvature of field (the edge a little fuzzy and the center sort of sharp).
The bluish edge is common to most fisheyes and is caused by internal flare within the hemispherical front element.
Advantages are being able to use on most cameras and lenses, even those that are not removeable from the camera.
I suggest using on a medium zoom with the APS digitals as you can adjust the center circle to different sizes.