I bought the sharpener from the Grace Company. It's about 12" long with a groove in it and you run your blade through it several times. I heard from someone on here that it didn't sharpen an already dull blade but did make a difference on the life if they used it regularly when opening a new blade.
I had a blade that was getting dull when I received the sharpener, so decided to try but didn't expect much. To my surprise, it was better and I am still using the same blade a month later. I recommend the Grace TrueCut sharpener.