I also regularly go to a Whole Foods with this system, it initially felt like a good compromise between "one slow cashier shouldn't hang up a lot of people" and

I also regularly go to a Whole Foods with this system, it initially felt like a good compromise between "one slow cashier shouldn't hang up a lot of people" and "people react negatively to long lines, even if they're fast-moving". The way this particular one works is with color codes -- there are four color-coded lanes, and when a cashier becomes available, they are announced by the system, which cycles through the colors. It has some failure modes. In the "dilute limit", if a customer approaches the lines and there's nobody else there, there's no indication of which color was last called or which is next, so they have to guess. If they guess wrong and someone else shows up and guesses right before a cashier becomes available, they might lose out. This effect goes away once the system acquires "memory", by having people in the queue who have seen the last cashier announcement. At moderate congestion, it can be hard to assess which lane is shortest, because people don't space themselves evenly, and sometimes go up in groups. People have a pretty strong sense of fair play, and I've seen people grumbling when the system breaks the expected FIFO dynamic. But, generally speaking, it works better than I thought it would when they first set it up.