Surprisingly well. It blocks almost all of the splatter from the back, and I think I get a little extra spray from the front (as the tire turns left and right) but not much.

I didn't have any steel rod handy so I robbed the strut off an old cruiser fender for the front, and mounted the back with an angle bracket from the rack. They turned out pretty good in my opinion, except for one zip-tie where I got in a hurry and forgot to replace with a bolt - I'll post a better picture later since you can barely see them from the side view.