Unless you need to use your phone for an extended amount of time away from home, not sure why you would need these devices. I have a basic phone cord in my car and simply plug it in to charge while driving. The battery lasts all day when charged. I keep it plugged in at home so it stays fully charged.
Remember that not everyone spends all day every day indoors or in a private car. If you're spending a day out and about walking, such as in a major city (or in a theme park, funnily enough, given the board this is), or traveling all day, or outdoors, stopping to plug in a cable is a time-suck, even assuming you can find an open charger, which is no sure bet. At WDW, especially, finding an unclaimed open power outlet in a park is nearly impossible.
In my normal daily routine I won't use up battery power in a 10 hour day, but in a theme park, or entertaining myself on a plane, the power draw is immense. Continuous use in WDW parks will normally kill my battery in about 5 hours.
One other thing: LABEL your power banks! My DD & DH managed to lose 3 power banks in 2 days at WDW a while back. I was furious with the both of them; not only did we have to scramble to keep our phones charged to stay in touch all day with just my battery, but it cost me over $100 to replace them all at once as soon as we returned home. I'm sure they probably were found, but none of them were labeled, so getting them returned was hopeless.
Also, BTW, buying a power bank with built-in cords is fine if they still have an older phone; you can just add adapter dongles, like these:
https://www.amazon.com/Certified-Li...ocphy=9022896&hvtargid=pla-1731812336619&th=1
... but I'm really not) who wanted an idea for the grandkids. - She's had trouble reaching a couple of my nieces because their phones are always dead.
