The optimization of the 21-35mm is for extreme sharpness, not unlike the 24-40 AT-X Tokina, which I strongly suspect is its cousin. Here are some throwaway shots at 35mm, which should show you just how insanely sharp this is (it will easily moire on an M240). Hopefully, you can see these at full resolution.
Distortion is mild, a +4 at 35mm if you are doing something critical.
I would note that this lens is a lot sharper in the corners with the 240 than a lot of symmetrical lenses are, in part due to its retrofocus design.