You don't need a vw device, trust me. I know a number of 3- 4-year ECF vets who use and love their eGos (having tried all kinds of mods along the way; I'm one of them). I'm not saying here that mods are bad--some of them are fantastic! I had a chance to play with a mini ProVari for a day--great device! But I don't need it; it was too bulky and too gadgety for my taste. I know my volts and my watts already and I'm perfectly happy with my small Twists and Spinners.
Don't worry too much about your ideal wattage; it will change with time and the kind of juice you use. You'll figure it all out in no time, once you hold the battery in your hand. If your vivis come with a 2.4 coil, start at 3.4-3.6v on your battery (that combo will put you between 4.7-5 watts) and see how you like it. If it's too cool, just increase the voltage gradually.
Oh cool Katya, thanks for putting my mind AND my pocketbook at ease
It will be ok to use it without the cover until I order one, right?