If I'm carrying around a giant battery I ought to be able to charge my devices from it, but it is silent on that front.

The design doesn't work if you have a mud guard or pannier rack. Also unclear how easily it is detached. Do I have to take it off everytime to prevent casual thievery? How do I take it off to charge inside? Does it have anti-theft bricking?

I'm struggling to understand who the target market is.

"How do I take it off to charge inside?"

It has a removable battery so it seems the mechanism is designed to be left on the bike.