Harbor Freight has a very good return policy. You can find it on their web site.
Personally, I wonder if one manufacturer makes blades and sells them to all the rotary cutter companies.
I would not doubt it. There are other sources of generic blades almost as cheap as H.F. $1.50 each is not a bad deal, but the postage is high for small orders.
I have been using H.F. blades in 3 brands of rotary cutters ever since they were first mentioned here. What a wonderful service that QB member did to hundreds, maybe thousands of us. I love them