There's generally two ways to do temperature control that I'm aware of. The first method is to use a wire, such as nickel, whose resistance significantly changes with its temperature. Once the desired resistance is achieved that correlates to a desired temperature, one can dynamically adjust power from a battery to maintain that resistance. The second method is to monitor applied voltage and current and based on the known heating properties of the substance being vaporized, one can dynamically adjust the applied voltage and current to maintain a certain temperature. In the first method, a measurement of energy applied or consumed isn't likely to be relevant to the temperature control. That's because you're monitoring the resistance of a wire that significantly correlates with temperature. In the second method, a measurement of energy applied or consumed can be relevant to temperature control. For example, let's say I want to heat 1mL of water by 1 degree Celsius. To do that, I need to apply around 4.2 Joules to the water. So regardless of what voltage or current I chose, once I know that I've applied 4.2 J, I can stop heating the water.
So what method is the SX Mini using? Probably the first method. The reason for this is that the second method only works if you have precise knowledge of a considerable number of factors (e.g., the volume of what's being heated, the exact thermal properties of what is being heated, the energy efficiency of the heating element). With the considerable variety of atomizers and countless formulations of
e-liquids, there's likely no way to easily determine all the relevant factors required to employ the second method in a variable-wattage regulated mod. In comparison, maybe you can do the second method in a pre-packaged e-cigeratte, because there you do have much more control over the operating environment.
So if the SX Mini isn't using Joules for temperature regulation, why provide it? One answer is that it's showing the amount of energy you're battery is able to supply. This allows the user to know how much they are going to get out of a battery before it needs to be recharged. In essence, it's like a puff counter, except that it's actually useful. First, rechargeable
batteries lose the ability to supply energy over time and use, so knowing the amount of energy the battery has supplied can be useful to knowing when it needs to be replaced. A second aspect is that the ability of a battery to supply energy is related to the resistive load it is applied to. So it may be useful to users to see how using atomizers with different resistance affect the amount of energy that a battery can supply. Finally, you might also be able to figure out a number at which it's time to replace your atomizers/wicks/
coils if you're using a consistent setup.
Finally, as to the idea of using Kanthal only in temperature control. It's resistance doesn't significantly change with temperature, so you can't use it with the first method described without super-sensitive sensors ($$$). You might be able to use it with the second method described, but as noted above that likely isn't feasible for a variable-wattage regulated mod. So chances are the 350J does not support Kanthal-only temperature control.
So what about twisted Kanthal/Nickel? Well, the thing to realize here is that the resistance of Nickel is much lower than that of Kanthal. Since the wires are in parallel, that means that all the current will pretty much pass through the Nickel wire and thus only heat the Nickel wire. The Kanthal wire would then have to absorb heat from the Nickel Wire before it could be of any use. This obviously delays the twisted coil from reaching the right temperature as fast as a pure nickel build. The presence of Kanthal will also make the temperature regulation less accurate. Personally, it doesn't make much sense to me to take this approach. The only benefit I can see of using Kanthal with Nickel is just to provide a physical structure on which to use Nickel wire, as some people find Nickel wire a bit difficult to work with.
