These coins are absolutely perfect for just about anyone's game— there's no way you couldn't find a great use for these!
Personally, I use them a "Luck Points". If a player rolls a 20, they get a Copper d20 Coin which can be spent to reroll any one roll for themself.
If they roll a 2nd 20 before spending the Copper d20 Coin, their coin upgrades to this Silver d20 Coin which may be spent for themself or an ally to reroll any one roll.
If they roll a 3rd 20 before spending the Silver d20 Coin, they reach the final stage— a Gold d20 Coin! —and may spend it for themself, an ally, or an enemy to reroll any single die roll.
My players LOVE these coins!