In a basic way a provari and an ego will do the same thing as they fire the atomizer,
what a variable voltage/wattage mod gives you is the ability to change the power going into the atomizer changing the taste and vapour production alowing you to find your sweet spot and also giving you a battery meter and ohms reader.
some if not most people like the aesthetics a mod gives you and given the right set up and battery they tend to last longer than an ego