I saw those can openers at Target for about $10 and was finally able to score one at my local thrift shop for $4.
It was able to open an 8oz can and the larger 12oz can but I had to first remove the metal guide loop thing. You can just pull the metal guide straight out with a pliers and it's easy to put back in place when you're finished.
I held the opener in my left hand and applied a slight rotational force by turning my wrist clockwise. This helped to keep the cutting blade in contact with the can. I turned the handle clockwise with my right hand. To help guide the can, I sort of rested the can against my legs because otherwise it started to slide out toward me.