Pizza 4 Pesos
While I understand this concern. I feel that this will last as long as people pay heed to it. After that, the program will go into the shade as people move on. I also fear that this could get your adverdge waitress or waiter confused or open the doors to those who could charge a bogus exchange rate to fool customers.
On a personal note, I have some MXN lying around somewhere in my coin collection. However, since Mexico revalued the Peso some years back, I doubt I can use them to buy a gooey, cheese, pepperoni, and mushroom pizza! If this pizzeria offered to accept these fine currencies, then we could talk.
Such is life.