The TP-Link TL-MR3420 is a 3G/4G Wireless N Router that allows users to share a 3G or 4G mobile broadband connection, usually via a USB modem, with multiple wired and wireless devices. It creates a Wi-Fi hotspot and includes a WAN port for a traditional internet connection, providing an "Always-online" connection through a backup strategy. Key features include 300Mbps wireless speeds, WPA/WPA2 security, a WPS button for easy setup, and bandwidth control for managing network resources.