"I don't need one for my tinned tomatoes bought cheap, as they are not cheap tinned tomatoes, they are premium tinned tomatoes with a built in ring pull..."
...and that's another story! What a pain some of these ring pull cans are. Its almost impossible to do it with a one finger and you still need some sort of gadget to get hold of the things, most of which are pretty useless. I find the easiest way is to put a fork or spoon handle through the ring and with 2 fingers each side it comes off quite easily.
We use the same style can opener as Covergirl. We've had it years. Have you looked carefully around the cutting wheel of yours lately. Its amazing how much 'crud' builds up despite washing up.