That would likely be me.
I got one years ago to have my own secure WiFi on the go--the old iPad, school chromebooks, etc., all got connected. It is a small device, very thin, likely as thin or thinner than most phones. It is your own personal mobile hot spot.
Newer phones have that option to add the service in rate plans in a mobile hot spot. So lets say you had an older tablet that would not have a separate data plan, with that hotspot, you could get internet on the old tablet.
When I am in an area where the service may be spotty (or inside Target even shopping with my different apps), especially if I remember to turn on the WiFi as I enter the store, even if the primary signal on my phone from my carrier is weak, the boost from my little WiFi will almost always be strong enough to offset network crashes.
Unless you are only hardwired at home with computers, you likely have a home WiFi. Just like that, the pocket WiFi has two different frequencies--2.4 and 5.0 mega Herz I think. I switch between the two as required.
So my mother-in-law has the plug in port adapter for her car. Traveling in recent months through some mountains, there are just some places where nobody gets good service. (On a vaca, one son without a helmet had a simple fall getting of a ski lift, tangled up with his snowboard. Concussion. On the ambulance ride to the regional hospital, even the EMTs had spotty connections on their communication line to the ER, back and forth.
I like the convenience of faster uploads with some apps given that WiFi boost. And my apps are also less likely to crash with network error messages that causes me to reload often or need to hit submit again.
They charge fast. The charge lasts a long time generally compared to my phone battery usage. I only turn my WiFi on as needed when needed and am careful to turn off the WiFi capacity on my phones too when not intending to use it so I have no surprises with data limit overcharges. That would be a very bad thing on my mobile bill.
I hope this helps. Not recalling, if revealed, what region you live in, maybe it is a good investment, but maybe it would not work as well for you as it has for me.