I can't see how they keep the crud out: surely they act as bellows and cause suction at the top end for the noodle, drawing water in?? (Assuming the rubber bit touches the other brake. Am I right in thinking that if you use them you should set it up loke this? ie they act as a spacer to indicate optimum gap between arms. Mind you, I can't see how this works either, given that frame differ so much.
Bucket. Much simpler!