It's a niche market. As the author states in the article,
"Hotspot devices are ideal when users don't have a smartphone with hotspot capabilities, or they have a hotspot-capable phone but is limited to the number of connected devices. They're also great if you want to leave your hotspot-capable smartphone open for sending and receiving calls."
So while most people will be happy with just a smart phone for tethering, there are some who may find this device useful. For example, if you want LTE speeds for your whole family but don't want to get them all LTE speed phones and you don't want to drain the battery on your phone. Or, if you want to take your phone with you but you want to leave the LTE internet network in your car for your wife/husband and/or kids to use.
This also makes a pretty good home router replacement. It's a bit pricey compared to a home router/cable internet, but it allows you to pick it up and take it with you if you want. For example, if you have an old iPhone that doesn't support 4g LTE, and can't or won't upgrade yet, but you still want internet in your home and stuff you may consider getting this device.