Stevia is the "all natural" sweetener that comes from the leaf of a plant that grows in Paraguay, Stevia rebaudiana. Stevia is a great sweetener for fruit and vegetable juices. But the powdered stevia you buy as Truvía or you see on the label as rebaudiosides or steviol glycosides or E960 is not entirely natural. In fact, it's about 99% artificial but as artificial chemicals go, the artificial chemicals used to make powdered stevia aren't especially bad.
South Americans have used stevia leaf as a sweetener for centuries. You can just pop a handful of stevia leaves into your tea and a few minutes later the tea will have a sweet taste with anise or licorice aftertaste. Not everybody cares for the taste of anise or licorice, so about 20 years ago manufacturers in Japan mastered the process of extracting the sweet-tasting rebaudiosides (also known as steviol glycosides) from stevia leaf with industrial solvents. You can still find natural stevia extract in liquid form, but these products all have the anise-like or licorice-like aftertaste.
Both the benefit of using powdered rebaudiosides and the downside to using powdered rebaudiosides is that they are about 350 times as sweet as sugar. If you were to use rebaudiosides uncut, you might find yourself somehow trying to measure out 1/350th of a teaspoon of stevia to get the right amount of sweetness in your morning tea or coffee. A tiny jiggle of the stevia jar and your drink or juice would be unpalatable. To avoid this problem, stevia packagers mix the rebaudiosides with other sweet powders.
The cheapest way to package stevia is simply to mix it with powdered sugar. The problem with this approach is that consumers object when they discover manufacturers add sugar to sugar-free sweeteners (and labeling laws in most countries permit labeling 0.5 gram or less of actual sugar per serving as "sugar-free"). Some companies choose to blend stevia with xylitol or erythritol sugars instead.
Xylitol isn't a horrible thing to put into a beverage. Made from tree bark or corn stalks, xylitol has about 20% of the calories of sugar and it blends with stevia well. A gram of table sugar mixed with about 10 milligrams of stevia powder has 5 calories. A gram of xylitol mixed with the same 10 milligrams of stevia powder has 1 calorie, and a low glycemic index to boot. The problem with xylitol is that it absorbs moisture from the air and the packet has to be lined with foil to keep the sweetener from becoming lumpy. And when people consume too much xylitol, they tend to get gas.
Stevia powder manufacturers in Australia found that another kind of "semi-natural" sugar called erythritol works a lot better than xylitol. Erythritol is made by fermenting corn or sugar beets. It also occurs naturally in pears, but pears aren't used in making it. Erythritol has slightly fewer calories than xylitol (and lot fewer calories than sugar). It won't gas stomach upset or flatulence. It doesn't absorb moisture from the air.
A peculiarity of erythritol, however, is that it absorbs heat when it is dissolved. Adding a stevia and erythritol blend to your coffee or tea cools it down. Adding stevia and erythritol blends to baked goods inteferes with the baking process.
Adding stevia and erythritol blends to fruit and vegetable juices, however, just makes the sweeter. If you like the added sweetness, there is no reason should not use this kind of stevia. If you want to add an anise or licorice taste to your juice blend, however, use liquid stevia extract drop by drop, being careful not to add too much.