The only reason I would ever go back to prebuilt atties is if I was out of Kanthal! I shudder to think how much money I have spent on attys over the years!! But hey, they kept me off analogs so I shouldn't complain. But financial benefits aside, the RBAs are just superior in every way.
Someone else will have to answer the technical aspects of this. I think it has something to do with PWM and amp limits or some such voodoo. But anecdotally I can say that the Vamo gives so much more "oomph" and flavor than the Twists did.
Here's a quote from another thread that may help, but someone else more qualified than me should answer your question.
"I'll never understand why the voltage matters at all. It's all about the taste. However, as I understand it, if you put to low a resistance on a twist and set the voltage high enough that it can't handle the amps, it's fire with the voltage it can deliver. So, if the amp limit is 2.5A and you put a 1.5 ohm DC on it, you can crank it to 4.8V but, it's going to deliver 3.75V. That's the most it can do. "