DIY battery powered Top Handle (45$) for Sony a6300, a6500 (and A7R II, A7S II, RX10 II)

What do you guys think about this battery powered handle ? awesome or stupid ? message from a reader : About the battery capacity - 5000mAh@ ...  is basically the same as 2500mAh@ ...  Therefor this powerbank has about  ...  the capacity of FW50 battery (s