Turnigy Jump Start battery to power multi's? Why not?

[Revs]

So I';m browsing Hobbyking for batteries and I see an ad for the Turnigy Jump Start Mobile Power Station. It peaked my interest so I clicked and had a look, but when I got to the specs I couldn';t quite believe my eyes.

This is a 12800mAh 3s battery that weighs 387g!

So to double check I went and looked at other large 3s batteries to make sure I wasn';t going mad and surely enough a 6400mAh 3s weighs over 500g. So my question is; what';s the catch? Is there any reason we can';t use these in out multi';s?

[Revs]

Just noticed it';s got a built in torch, too. And how handy would the ports be for powering peripherals! FPV gear, LEDs, etc.

[Revs]

Found the catch

Apparently it';s a 4200mAh.. 3 cell.. which of course means it';s a 12600mAh battery  not!

[blankers]

Everything on the hobbyking ad points to it being a 12800mAh battery 

[Revs]

I know, very misleading. It is about the weight and size of a 4200 3s though. The 12600mAh was referred to as ';aggregate capacity';.