I was in your shoes 1 month ago, and decided on the VMAX, since then, I now have a Provari mini, and contemplating on getting the ZMax,
I like the VMAX, just ensure you use high ohm carts on it since it burns hot, but in hindsight I wish I had gotten the ZMAX now, since you have the option to use Watts instead of voltage.
Where this benefits is, say you have 3 carts, a 1.5 ohm, a 2.2 ohm and 3 ohm. with a vv device each time you swap the cart you have to set the voltage to match the correct power output you prefer. The ZMAX wattage output mode allows you to set the Watts, (Most use 8 - 9 watts) which will then automatically set the voltage to you cart ohm reading, therefore effectively only needing to set the voltage once. Additionally the ZMAX uses 1 18650 battery instead of 2 18350 batteries the VMAX uses, which according to many, is a lot safer.