Visited a coffee shop in Boise that had a crazy simple loyalty system

Honestly, they just had a jar of wooden tokens by the register, and you got one with every drink over $4. After you collect ten, you trade them in for a free drink and they stamp your name on a board behind the counter. Tbh, the line was out the door and everyone was talking about their tokens. Has anyone tried something this basic for customer retention and did it actually work?