I've been happy with Vivi Novas and Vivi Minis and had no problem with anything except they are e-juice hogs (but I DIY much of what I vape, so extra expense is trivial).
Normally, I screw these into eGo T batteries with their regulated 3.2 volt output. I also am certain I'm using genuine Vivi Novas and Minis. Forgeries are common, so beware, especially if the price is too good to believe!
Just for grins, I've been vaping a Vivi Nova (and a few days ago, a Vivi Mini) on a LavaTube. LavaTubes allow you to adjust the voltage in 0.1 volt intervals between 3.0 and 6.0 volts. You can also get a readout of the resistance of your atty, carto or clearo.
While using a very clear e-juice (VaporRenu menthol, double shot, 80% PG / 20% VG and 18 mg./ml.), I've discovered that Vivi whatevers are quite sensitive to higher voltages. Specifically, I get poor draw and flavor, plus a hint of burnt taste, when the resistance is 2.4-2.5 ohms and the voltage is more than 3.7 volts, and when the resistance is 2.9-3.0 ohms and the voltage is more than 4.0 volts. In any case, if I go higher than about 4.5 volts, the vapor is nearly to totally unvapable.
Clearly Vivi devices are very voltage-sensitive. And I suspect that if you're running thicker (more than 20% VG), darker (darker than a very light beer) and/or cloudy e-juice, you're going to have troubles unless you keep that voltage down. Running the LR (1.8 ohm heads) on non-eGo batteries, which typically crank out 3.7 volts, would be inadvisable, IMO. Same goes for mechanical mods, like Reos, which run 3.7 volt batteries.
