That device looks to be more of a gimmick than real power.
You can get a 50,000mah pack with 100w inverter for under 200, then add a 200w solar panel for under 200, and have one hell of a portable power station. You can even use the car charger to your mavic and skip the inverter to save 50 bucks or so.
Goal Zero has the stuff to do it, but they cost an arm and a leg, so I did the same using Amazon stuff from China for a lot less money.
I run the 50,000mah pack for a whole weekend without the solar panel and still have power to spare. I think my pack might be 60k now that I think about it. Still really small and light at only 3-4lbs.