You should have a look at the website of the company actually selling the turnkey technology that is prepackaged on multiple brands of retail-oriented wi-fi routers.
Notable is that the information doesn't just stay in the store, it is collected and aggregated by the company's cloud service. Conceivably they could track your movements to and between any location using this service, with no advertising or warning of it's presence at all. It can be another Google Analytics, where the service represents itself as provided for free to stores to help market to your customers, but it is actually part of a larger data gathering campaign.
There is privacy-regulation-scale potential here, they can collect metrics that a particular user went into the mall, walked by Radio Shack, went into Bed Bath and Beyond for about 15 minutes (tap your phone here to pay...), went back into Radio Shack. Then they came back to the mall a week later, after going to the library, the mall across town, the coffee shop, in this motel in another town town, and in a hotel in Hawaii. They paid for wi-fi service in the coffee shop and in the hotel, so BTW, here is who they actually are.