I LOVE MY BLOC LOC RULERS. I used someones at a retreat and came home and ordered them. I don't know what size I have but one is smaller, probably 3 or 4 inches One is a little bit larger. I won a gift card to a shop that is about 100 miles away. Their website doesn't have much on it but they did have the rulers. I love, love them. I would say a larger one is a little bit awkward to use on tiny blocks.
Hope your back is better soon.