I think the main difference is simply this: do you want the option to use a mech (no voltage control) or not. Any mech with a kick in it will operate like a solid VW device, however, as time has proven (I'm not trying to start ANYTHING here) - there are mods out there that handle a regulated vape with much more consistency, such as the Provari.
So, if you go with the bombshell + kick - you have a decent VW device, and the option to get into purely mechanical, should you decide.
If you go with the Provari you get arguably the best VV device that will last you a lifetime, work as promised, BUT you will be limited to 3.5 amps which will not run an atomizer under 1.3ohms.
To me, that's the real difference here.