[witek]

Often, a loyalty card is nothing but a piece of plastic with a number printed on it. For example, for airlines and hotels I just give them the number, they never need to see the card.

However, if you mean a gift card with pre-loaded money, things may be different, but then it'd probably be a similar reaction if you tried to use Coin instead of a proper debit/credit card?

[michaelmior]

I'm just thinking about the reaction I would get if I walked into my grocery store and handed them my Coin. I'm not sure they would take it. Debit and credit cards may be a problem too, although they're diverse enough that unfamiliarity is less of an issue. Plus, you can handle the card yourself in many transactions. Usually loyalty cards need to be given to the merchant.