It’s no secret that it’s cheaper and easier to keep current customers than to find new ones.
An extension of that for many businesses is that their most successful form of marketing is through their current customers. Call it recommendations, word of mouth, even viral…the concept’s the same. People will trust their friend’s (your customer’s) opinion far more than any piece of marketing you send them.
This leads numerous companies to figure out how they can “get” their customers to talk about them. Many times this looks like trinkets/cards or other collateral that they can pass on to their friends.
It seems to me that a better tactic would be to give them something worth telling their friends about.
Make their experience with your company so great that they can’t help but tell their friends.
It’s probably cheaper than a bunch of keychains.