I recently obtained a nice 29er which I plan to use as often as possible. However, when it rains I would like to keep my backpack and my face clean. Shoes and pants can get dirty, I carry spares for those. I was looking at those little mud guards that attach to the down tube, are they good enough to keep a clean face? And for the rear, is a seat post mounted plastic affair worth using? Please let me know your experiences if you are using these on your bike.