Not only does it work on full frame (as a 15-16mm f/2.8, unless you want a hard vignette in your image), but it is actually pretty sharp!
Check my tests here:http://www.similaar.com/foto/lenstestsff/lenstestsa.html
My test chart is not huge, so with such a wide angle lens this is a very short focus test. In these conditions, it's not the sharpest lens in the test, but even in the extreme corners it is better, for example, than the Canon 24mm f/2.8, and similar to many other lenses, including my beloved 35mm f/2.8 (which I regard as a very sharp lens even in the corners).
Trouble is, a lens can be very sharp when focusing one foot away, but blurry when you focus at infinity. I'll have to test the Tokina in the field, but based on these results, I'm already quite impressed. If it keeps its sharpness when focused at infinity, this may be the best bang-for-buck 16mm f/2.8 prime you can buy for a full frame camera.