Simple answer: Kick is a chip that goes between your battery and atomizer to turn a mech mod into a VW mod.
Long answer: It allows variable wattage via a potentiometer mounted on the top half of the PCB assembly. It requires an additional tube extension, unless your mod telescopes. It MUST be placed between the atomizer and battery, otherwise you'd fry your kick chip. As mentioned, it has a voltage and resistance cut off; it wont fire below a certain resistance (depending on the chip) and wont fire once the battery drains below a certain voltage. The wattage range depend on the kick chip, some are 5-12, others are 6-15.
In the event of a hard short, I think it acts as a fuse aswell. Personally, any time I run a tank on my mechs I use a kick.