It has a 21.6 Wh battery. You can easily get a power bank 3+ times this capacity, thus can last 4x longer. If anything, I would rather have that weight in my pocket or backpack than on my head, all things considered.
Anecdotal, but on the last few flights that I've taken. I was told that you can use them, but you can't charge them on the flight. This was inside the US, American Airlines, and United. I can't speak to the other airlines.
I believe the restriction is on charging devices out of sight (in luggage, seatback pockets etc).