One woman's mistake is another woman's "can't live without". I think the only ruler I have regretted buying was the Eleanor Burns flying geese before I discovered the no waste method. But, I have used it and I am sure I will again.
My aunt died this fall and my uncle brought us a bunch of her stuff. My sister actually took some of the rulers and handed to me and said,"I don't have room for this at my house. You take it and I will know where to borrow it." So, now I have a 20" square and the biggest triangle I have ever seen.
Right now my biggest regrets are pre-cuts. They stump me and just lay around looking pretty.