I haven't used it but my friend uses the
Square In A Square ruler from Jodi Barrows. She made a lovely Storm at Sea quilt for my daughter using it, and said that it was easy to use. She also said that there was quite a bit of waste but that the scrap pieces were large and would be useful if you are a scrap quilter (she is not). But as I said, I haven't used it personally....
Alison