If you get a mechanical mod there is no voltage regulation.
you have to use a low resistance coil on a mech because when the battery is fresh you get 4.2 volts and the vapor is stronger. as the battery dies the vapor dies with it. when the battery is 3.7v volts you get 3.7volts to the coil. and nothing can change that. so if the coil is not tuned correctly the vapor will be very inconsistant.
along came the kick, it is a regulation device just for mechanicals. you drop it in on top of the battery and set the voltage/wattage you want, now you will get, say 9 watts from fresh battery to dead. Just like a regulated mod.
It allows people to buy mechanical's for their form and beauty but still have a regulated device for a consistent vapor like a VV device.
they are not used or needed for a VV/VW device. mechanicals only.
for the most simple explanation look at it like this- you buy a mechanical then rip the electronics out of your Itastevv and stuff it into your new mechanical.