Our store had only 2 packs so I bought them and ordered more online as the store would not special order them, only told me they had more coming in this week. So I called this week and they are holding 20 packs for me to pick up on Monday. I tried the ones I bought and they work wonderfully. I cut thru 8, yes 8!! layers of quilting cotton fabric with only a second stroke to catch a few missed threads!!!! When cutting 4 layers, only one stroke was needed and there was minimal cutting into my mat. A bit less than with my other blade I'd say, because it needed less pressure.
The HF blades seem a little thinner than the Joann's blades, and I don't know yet how long they will last. But my son did a lot of cutting for me with the HF blade and it is still going strong.