In my experience with metal cards they’re multi-functional.
They can be used to pick the dirt out from under your nails, as a ruler, to cut soft objects when you don’t have a knife to hand, to undo the notch thing on the hoover when I need to get the brush bar out, and plenty of other things which I can’t think of right now.
I haven’t yet used one to try and open a beer… I’ll give it a go and report back 
