I have a gazillion and none of them work as well as the blades I get at Harbor Freight. They are in packs of ten for $2.98. They are replacement blades for a utility knife and have a sturdy flat side that you can hold onto pretty easily. They have a point that fits under the seam and because they are so sharp they glide through the seam like butter. I used to use box cutters from Delta Air Lines that were easily 25 years old, but when they dull that is it you have to throw them away. You cannot get box cutters like that since 9/11. I've tried every commercial seam ripper on the market, or at least it seems that way, and the razor blade is by far the best. Of course if I didn't make mistakes then I wouldn't need a seam ripper; however, that not being the case I reccomend the blades.