I think a caribener attachment would be a good idea, so you can hang of your backpack or belt would be a good improvement.
Ain't no one want to out that case in their pocket, where as you might do with just the power bank n cable.
I always carry a lead with me, cos I don't have a power bank, but at least I can charge on a wall charger (plenty friends work in town, I can borrow a charger from).