Normal blades, usually a 2-1 or high lift containing a taller sail has only one purpose; to move as much air and clippings OUT from under the deck. The reason why your mulching kit has different blades is that they will lift the grass just enough to cut and then re-circulate the clippings under the deck without trying to move them out from underneath Obviously the plug completes the package by allowing the clips to stay under the deck to get re-cut over and over. A high lift blade with a plug will result in a lot of blowout and clippings piling up on the discharge side of the deck. Even with the kit installed correctly, be advised that mulching only works well when conditions are just right. The grass must be as dry as possible, you must remove only 1/3 or less of the grass length and you cannot mow at full speed. Doing this as I have described will leave a nicely cut lawn with small clippings recycled into the turf to provide fertilizer. If you follow my advice and you still get a lot of visible clippings or some clumping, either slow it down or mow more often. As for blade sharpness, the blade isn't supposed to be "razor" sharp. As stated by others, blades that are really sharp will wear/dull faster.