Stevia is a natural sweetener that has been generally recognized as safe by the United States. Tens of thousands of studies conducted in Japan demonstrate its safety and they've used it as a dietary supplement for decades. Various cancer research institutes have also ran large-scale human studies that support its safety. Do not confuse Stevia with aspartame, saccharin, and other artificial sweeteners.
Stevia doesn't have the same mouthfeel as sugar and has a tendency to develop a bitter taste above a certain quantity but I attribute that to the typical American sweet tooth; I have no trouble flavoring drinks with Stevia because I prefer about half the level of sweetness that a commercial product might otherwise have.
The first ingredient is "sugar" but because the serving size is 1 tic tac each serving contains 0 calories, including 0 calories of added sugar.
The magic of rounding!