I too only change out my blades when they are not making a clean cut cosistantly. I will too at that time clean my rotary and then add a couple of drops of oil on the new blade. Sometimes I will do the cleaning and oiling on a used blade if it seems to slow down or have a bit of a pull to it. Usually a lint build up-even in the cutter:)). I agree that sometimes they seem to last a bit while others might not. Could be the differences in fabric you use. I always keep the refil ready in my sewing drawer-just in case:)). Skeat