i just started shaving with a de blade set up. the blade that came with the razor was a merkur. got 3 complete shaves and then on the 4th shave i got a horrible experience. blade was pulling my stubble and i had to throw it out. now i am on my 5th shave with a muhle blade, showing it's age, shave not as close as first few uses of blade. my point is, for some reason these double edge blades vary greatly in their lifespan. you will know it is time to replace your blade when it starts tugging on your stubble or you need too many passes to get a close shave.