i dont think there si an ego threaded
rba. none tha ti know of anyway. there are slimmer RBAs that will look nice on an ego, like the A7, slim A7, vision eternity, and possibly even the phoenix will look great on an ego. you just need the "small
tank cone/sleeve" to make it flush.
also, check to be sure your batt has short protection. i know twists have it, but im not sure if it works in such a way that you can still use the battery after a short. it may just protect the batt from exploding, then render it useless.
personally, id pick up a vamo kit or a mech mod kit. lots of em are coming with RBAs these days if you check around.