I went to a Sue Hausmann seminar (America Quilts) just a couple weeks ago. She had several sizes she passed around. I thought it was a rather nifty idea but they were pricy, so I didn't buy them.. I'll be glad to hear what others think of them. I've squared up my blocks with a regular square, and it does rock a bit... but I haven't thought that was too much of a problem. Of course we thought cutting with good scissors was great until the rotary cutter came along.. So what do I know?