At 8mm, it should still produce a fish-eye effect on a crop sensor body, but to a lesser extent.
Otherwise, the FOVCF leaves out most of the distortion.
It's a nice lens, and a great idea, but to be honest, I don't see this being very practical - as with most fish-eye lenses. The difference between this and the 15mm, though, is the price difference. I doubt it will be very popular, as in most cases the regularity of its usage does not warrant the price.