I've never had a problem with them and at a buck a piece I can afford to toss one if bad..or take it back. Only time I did have a problem was putting two blades in at the same time until I realized why. I have used the blades for several years now without a problem and I cut tons of fabric.
I am in the process of cutting fabric for my second quilt and I am still on the same blade from Harbor Freight. Yes, you may find a bad one, but for the most part, I'd never buy blades from Hancock's or Joann's or other fabric shop. I'd go an extra mile for Harbor Freight. I have been using them for about three years now. Can't complain one bit. Edie