I've purchase close to a dozen of these airstones from Aquarium Co-op - pretty much one per each sponge filter I've purchased. The oldest ones have been running for 6+ months, and haven't needed any maintenance in that time.
These airstones I ordered fit perfectly inside the aquarium co-op sponge filters!
Truthful to its name never clogs! I've just bought some more for my hospital tanks and for my new fry project!