It depends on how much it rains in Wisconsin. Generally the answer is yes. Fenders keep the water where it should be.
However, I used to live in the desert. Rather than a fender, I just kept a newspaper folded on my rack and bungied down. It stopped most of the grit and mud. Considering that I would run into rain there maybe once or twice a year, it was adequate. Now that I live in Arkansas, I love my Freddy Fenders.