I love my eGo, too, but as it only delivers, like all joye 510s, 3.1v, a 901 on 510
batteries delivers very cool vapour. Mind you, that's nice for some very few flavours, but probably most people won't like it for most flavours.
OTOH, a 901 on a mod is not a problem at all, no 3.1v-problem there. And the KR8 batteries fit out of the box, too. Very convenient.