lens pen

Ordered a $3 lenspen knockoff off of ebay figuring it was the same thing as the calumet store-brand model (looks the same).

Stopped working after a few uses, I'm guessing the carbon or whatever is in the cap ran out and the felt on the nub is all stamped down.

Anyone else use these things - is it worth shelling out the $20 for the actual lenspen brand version (I think there's a slightly cheaper Nikon-branded model)?