I had horrible luck with Harbor Freight blades. They skipped and wouldn't cut worth a darn and yes, they wreck your mat when they are so dull. I have been reading mixed reviews on them all the time. I've come to the conclusion that different Harbor freights, sell different brands or kinds of blades. All of us quilters know a good blade from a bad blade, so it has to be that they are not all the same. I tried every one in the package and they all were not sharp enough to cut without skipping. I even have a blade sharpener and tried sharpening them, they just were low quality blades.....