The only difference is how they look. One factory brougt out the "version 3" Vamo - its just a different look on the body of the
device. Edit: The V3 has a removeable top cap so you can use a Kanger T3 without an adapter. (Sorry - forgot that before).
I prefer the Vamo v2 myself, and have two of them.
So - whichever you like the look of is the one to get.

You won't be missing out on anything.