A Wi-Fi modem with LTE Support looks like the usual router. It differs because of the LTE support. While you need to connect a normal modem with a cable, a Wi-Fi modem with LTE instead uses just wireless internet from your operator. It's similar to sharing a connection with your smartphone.
The ASUS 4G-N12 B1 complies with the 802,11b (2,4GHz), 802,11g (2,4GHz) and 802,11n standards, and this lets you achieve speeds up to 300 Mb/s. The 802.11n support is of particular importance because it allows for communication at speeds up to 600Mb/s, which is the current maximum on a 2.4GHz frequency.