I had not seen the square mat before I bought the circular one which is on the right in the top row of the link at the bottom. I got it for $47 at a craft show. However, judging from the prices on the other mats there would have been no sale if I'd seen the others first. The only problem with the completely circular one is that it has a tendency to swing a bit too easily and as it is raised about 2cm off the table it is difficult to cut and rotate pieces that are larger than about 12".So it is really best for small, fussy cutting. Hope this advice is helpful to folk in my neck of the woods.
http://www.victoriantextiles.com.au/...y:Cutting+Mats