I agree with Caspharm, I too ordered their expandable ruler set, they are clumsy, and cheaply made which I suspect will quickly get chipped by your sharp rotary cutters. I do use their Add-A-1/4" and Add-a-1/2" extensions though for pattern making.
I was at a quilt seminar recently and saw a demonstration of a better ruler set of high quality and better design presented by a company called PM Quilting; I will be spending my gifted Christmas money on them.