I think I've figured out what they're going for. Device A connects to $HOTEL / $COFFEE_SHOP Wi-Fi, then shares its connection to the router via Ethernet. The router than shares with your other devices (I'd guess max 5 at a time to prevent overstuffing Device A's connection.).
Assuming they can get #FCC approval, the next iteration should support putting 'Device A' behind the GL-AR750S with the others. The router itself should be capable of connecting to another #Wi-Fi and allowing a device on the network to do the public Wi-Fi's login routine.