I remember hearing somewhere that toothpaste can also be used as metal polish. Is this true?
Actually, the cleaner/polish is made in Germany and it’s distributed by Star Clean in the U.S.A. It comes in a 150 ml (5 oz.) tube and retails for $18.99.
It’s a white-colored substance with the consistency of something like a cross between yogurt and Colgate toothpaste.
The directions are slightly confusing; the box adds a “rinse” step after the application, but the Star Clean tube says to use a wet sponge to apply it, then wipe it dry and you’re done. Rinsing works well if you’re using Star Clean to polish chrome wheels, because by time you finish a wheel, some of the Star Clean has dried, and the water works best to clean it off before wiping.
So, yes, it is. 
It does work - I wouldn’t try it on an expensive yoyo though, for that I’d opt for a product intended for the purpose. But maybe useful to breathe some life into a beater. Try it on a piece of scrap metal first (like a soda can, which is also made of aluminum).
I’ll try it on my Black Knight.