The picture I'm seeing of the firely at Liberty Flights looks identical to a Ego/Kgo/Riva type batt. The skirt on a "stardust" just covers the threads that would normally be covered by a cone. A 510 to ego adapter raises up the conection point on the battery to allow an "ego" type carto to be used on a battery that doesn't have room to accomodate the recessed connection (skirt).
This is the description at Liberty Flights:
"Upgrade your 510 device with the Firefly, the newest in EGO style PV's. These batteries should only be charger with en eGo/Riva style fast charger."