A 4G router will give you speedy access to the internet simply by inserting a sim card and powering on the device. Great for people who do not have access to the NBN. These devices can also be used in a hybrid scenario - connected to a broadband network via the WAN connection so they can also be used in a fail over situation.
A TP-Link MIFi device, sometimes referred to as a Wi-Fi hotspot, is a portable, pocket sized router with a battery. Simply insert your SIM card and take your mobile, sharable network with you anywhere you go.