Ordering isn't the bottleneck at In n Out, it's the food made fresh, sometimes for custom orders. The menu itself couldn't be much simpler. The kids taking down the orders work quickly and are always at the end of the line. That they're friendly humans and not a confused AI is an added benefit.

On the other hand this should work for McDonalds, where nobody's expecting friendliness or much of anything; it's basically a feed trough.