You wouldn’t want to exchange a suitcase full of cocaine for a suitcase full of gold and then discover, long after the purchaser had flown away, that the coins were 90% pure gold instead of 99.99%.

As long as you trust the ECB to keep inflation down, it probably makes more sense to stick with eurobills. It’s a lot easier to inspect a modern bank note than assay an allegedly gold coin.

Silver is probably better for day to day zombie apocalypse transactions.