I'm just using it on my Inferno, which is 3.7v. It came with 3 different heads, I think they are 1.7, 2.0,and 2.8, but I'm not for sure. Don't have them on me at the moment. I've been using a 4ml tank with a 1.5 dcc polyfill cart. I love the ease of it, but it mutes the flavors. I tried a CE2 cart in it, but it seemed to either flood or burn, so I gave up. I'm trying to find something I like. I don't have a variable volt mod yet. Have been thinking of getting the Lavatube 2.0 when it comes out.
I don't spend much time with my Vivi. I prefer my RAs, DID clones and good ol tank/cartos. My SO gets most of the use out of the Vivi and she enjoys it, so that's a plus.