The cheapest blades (unbranded store blades) are almost always going to be pretty lousy.
I bought some blades here once branded as "Laser". They came substantially wrapped and looked as if they may be a decent blade....until I opened the envelope.
I could see from the way the edge was ground that it would not be a good idea to put these in contact with my face! I also read a post on this forum which seemed to confirm my suspicions. Therefore I tossed the blades in the rubbish without using a single one! Don't know what I was thinking of buying those..:s
The worst major brand name blade I have used was a Merkur. It probably would have been ok if my skin was made of rawhide.....