I love mine ... sharper and lasting longer than any of the expensive ones I got from big brand name companies. I have them in both my Olfa and 'orange and grey' one, the name is rubbed off.
I agree, maybe you got a bad batch. I figured mine were working so well cuz they had to be really sharp and strong to be cutting carpets ... compared to just fabrics.
So far the few packs of 20 that I bought have all been really great, I bought mine online last year when the quilters had a run on them at the local Harbor Freight stores.