The first time I got a beastman coin drop I was expecting it to go into the currency tab instead of the normal inventory. I was hoping they would be similar to FFXI's beastman seals where we could use them to enter special battles.

It would be cool if we could use them as currency as you suggested to purchase stuff from beastmen NPCs.

But at the very least maybe metal crafters will be able melt the coins into a usable crafting metal.