I'm very unsure that paying from planet A to planet be will become a thing in the next few centuries (for Earth), and by then there can be very different approaches to economy, and we might not be the ones to set the currency. After all, to accept payments in cryptos, the recipients must acknowledge their value. So for now, the only relevant question is about payments on Earth. And regarding that, huge money transfers can cost way less with cryptos than in fiat back transfers, but small-scale transactions are faster and way easier to perform using a debit card.