Using it while flying will be complicated by the fact that all airlines have banned the use of power banks. If the onboard USB socket isn't very powerful then you'll only get an hours' use.
Last I checked I'm allowed 100Wh of power bank on a flight. And for flights where that's not enough I'm used to having a (~100W) socket.
You're also not allowed to use them even if you do have them with you. This is all very strictly enforced with reminders at the check-in desk and several announcements before take-off.