I bought mine at a show. I was going to just get the 6.5", but they talked me into the 2.5", 4.5", 6.5" set. Boy, I'm glad I got the set!! While it is true that you can use the 6.5" ruler to cut smaller units, it is so very convenient to have the smaller ones the exact size of your patch. I have a small turn table cutting mat and can really rapidly trim lots of HTS with the exact size ruler.
I have never seen these on sale anywhere. Darn!