carter circle cutting jig

[FINER9998]

does any one have any first hand experience with this carter product:

http://www.carterproducts.com/product.asp?product_id=502&cat_id=76

this video makes it look simple to install and use:

http://www.carterproducts.com/circlejig.asp

seems like a worthwhile accessory for a reasonable price ($50). comments welcome.