You really can't beat the MVP 2 for the price & functions that it does are amazing, check out the MVP 2 owners group, just remember when your setting the volts you are actually adjusting the voltage so you will have a specific wattage at the coil.
VW allows you to set wattage to your taste liking & when you switch batteries, the unit automatically senses the resistance on the new tank & adjusts the voltage automatically.
The MVP 2 does both, just not at the same time, if your in VV mode it will fire the set voltage you selected regardless of the resistance it senses, now in VW mode it will automatically adjust voltage to maintain a constant wattage, so in short you can leave the VV set at 3.3 & forget about it, just keep it in VW mode & it's automatically set, just don't hit the voltage button or that takes it out of VW mode & into the voltage mode, where you would have to keep tweaking every time you change a tank or resistance. VW mode, set to your taste & that's it, no messing with volts. And this thing lasts me from 2.5 to 3 days & I vape pretty often. Thick juice or 80PG doesn't matter, also I rarely have to go above 6.5 watts.