Stevia rebaudiana is part of the sunflower family (Asteraceae), like the daisy. It is native to Brazil and Paraguay, where the local populations have used it as a sweetener for as long as written records have been kept.

After its scientific "discovery" by Europeans in the late 1800s, it became popular as an herb. As western nations began to produce more food at lower prices, obesity began to climb, so searches for sweeteners without the calories of sugar began. Stevia extracts came later than products like saccharine because it was expensive to get the important compound, Rebaudioside, in quantity. Though natives do chew the entire leaf, the U.S. Food and Drug Administration does not put the entire Stevia leaf, or even a condensed extract, on its safe list because of low blood pressure concern, whereas Rebaudioside is considered safe by every governing body, from FDA to the European Food Safety Authority (EFSA) to the World Health Organisation (WHO) and more.

Is it sustainable?

Since being placed on the GRAS list by FDA in 2008, Stevia extract has become popular in the $14 billion sweetener market because it has 200 times the sweetness of sugar, but in nature the plant does not produce large amounts (only 1%) of the steviol glycosides Rebaudioside M and D, which have more sweetness and less bitterness when used in commercial products than the traditional Reb A for personal use products like the brand name Truvia, so companies like Evolva have used fermentation to produce larger quantities of these sweet compounds in a more sustainable way. 

Stevia purchased by consumers is grown on small farms in tropical climates where the leaves are harvested and dried and then filtered with hot water into a purified stevia leaf extract which must have at least 95% steviol glycosides.

Will it help you lose weight?

The only thing guaranteed to cause weight loss is consuming fewer calories than daily activity burns. People who get rid of calories from sugar and don't add them with other foods will lose weight. 

Can it be harmful?

Stevia extract is GRAS by FDA so the only way it can be harmful is at poison level high doses, the same way vitamins can be harmful.

Is it a GMO?

No, though some steviol glycosides are produced using yeast, which is commonly genetically engineered, there is no yeast in any products. The same applies to arguments it might be an allergen. There is no yeast in the product.