Not true. Putting Olfa blades in my Fiskars cutter makes it turn like a car with a flat tyre. I have to use Fiskars blades in it, which have a completely round hole.
Haven't tried the Harbor Freight ones yet, but I know some people swear by them, whilst others hate them.

Makes you wonder if the owner is really that ignorant about quilting products are just greedy.

If the blades have the same hole configuration they fit.

You can get fantastic deals on blades here. I buy from them all the time and highly recommend them.
http://www.jhittlesewing.com/visitor/index_jhs.html

to quiltnchik: went to site, been looking a long time for reasonable prices, thank you thank you

Got 5 pkgs of blades from Harbor Freight for Christmas, haven't tried them yet. If (10 blades @ 1.99/2) for less than 10 dollars is cheapest I know of anywhere.And, some say are sharper than most.

Bella Boo, I have a Ofla cutter. Thinking the hole configuration is different from a Fiskars?

I did try out the blades from Harbor Frieght when they were first mentioned here. The ones I got did not cut very well at all, to my disappointment. I did find the right cutting mat does make a difference in keeping the blades sharp as long as possible. The smoother the mat is, the better. I got mine at a sewing/quilt expo as a show special. It is made in USA and three web sites are available. www.sewingemporium.com, www.seweasyproducts.com and [email protected]. These came off the sheet received with the mat....I do not have any connection with this outfit except as a customer. One small concern is that the margins are kinda wide, so I extended the grid lines with a fine permanent marker. No regrets in buying this product...it even has a five year warranty.