I bought a sharpener. It was a waste of good money. Have any of you heard of flipping your blade over (when your not cutting paper or poly)?? When your blade seems to be getting dull, take it out of the handle, wipe off the lint, add a tiny drop of oil, flip it over and put it back in. You can double the life of the blade that way. Saves money and a trip to the store to get a new one. Be sure to mark the blade in some way so you know you flipped it.
I buy a package of 5 blades at a time. They are expensive. I use the plastic container they come in (once it's empty of new blades) to dispose of the old blades. The container will hold alot more than the 5 that comes in it. I haven't found a use for the dull blades, yet.