Yeah i got the twist because of the adjustable voltage, though i'm only using about 3.8 or something at the moment, which seems fine, and i guess the other ego's/ecab are about 3.8 anyway? Still... maybe i'd need more with different attachments or juices, or even less. edit: actually wow, yeah, with juice change i'm now finding i need about 4.4 to get the same volume. I got the 900mah version because it was literally halfway between the 650 and 1000, sizewise, for some reason. The 1000 is about as much bigger, and only 100 more.
The ecab kit has a removable battery, comes with two, and extras are cheap, so you would only need one device, but that vaporchase guy had negative things to say about it.