I always end up with spare Euros, Pesos, Loonies (...everything!) after I travel, so I can appreciate this (somewhat) logical take on coin design by Mac Funamizu. The edges are a bit awkward, and maybe this could be corrected by adding a center circle. It'd be nice to have raised dots as well, for those that are visually impaired.
For now, I'll keep my spare change - at least the paper bills are something pretty to look at :)