i wouldn't get either of those.
lots of practice with a ruler renders them unnecessary.
also, i'm a bit of a klutz. i can see myself slipping and cutting right through it instead of properly along the slots.
accidental manicure, anyone? LOL
i have been kicking around the notion [pun intended] of getting one of the circle rulers, though.
i have the pack of individual templates, but this one goes up to 10" and offers more sizes.
a friend of mine let me try hers and i thought it was pretty nifty and more likely to be "me-proof". LOL
http://www.joann.com/easy-circle-cut/prd54225/