Tem control and variable voltage, these two working modes really make different vaping experience. The variable voltage function is a technology that has been developed maturely. In terms of temp control, it is lately developed. Regarding the specific vaping experience, most of vapers feel that temp control brings the more stable and comfortable feeling, also making temperature within certain range will not cause harmful substance production. But it seems to require more technology to achieve this function, more difficult than completing the variable voltage. Adjustable voltage or wattage is a simple thing, which can make you immediately enjoy vaping on your desired wattage. However, the terrible situation is that the temperature will rise as the power output proceeds and this unstable temperature state is not favorable to playing the best of e-liquid out. In a word, the variable voltage function brings the immediate power output and temp control is better to taste the flavour of e-juice. Eleaf iStick TC40W is a remarkable TC mod among so many tc box mods on the market, easy, convenient to use and slightly cheaper than other box mods. Also you can make a choice on other istick series battery with variable voltage/wattage function.Which one to choose is completely your decision. Happy vaping!