I agree with many of the other reviews that these are chewed up too quickly. Saying that, they don't have to be immaculate to work effectively. I change mine about every 2-3 months. With two dogs, I have to make sure that some stuff is picked up and small debris is what will destroy these. If you can't personally pick up the small debris, then you'll have non-stop issues. One of my dog likes to bring in wood branches to then chew on. The pieces wreck the brushes.