I've been using the H F blades for over a year and have never had a problem with them. They are sharp and I use way less pressure on the cutter when using them. Have noticed no difference in the mat. Is it possible that to much pressure is being used when cutting? Several friends use them all the time and so far no one has had any defective blades. I do use the Martelli cutter, that requires a round center hole in the blade maybe that makes a difference in how they perform.