Welcome to the forum. I grew stevia one year without knowing much about it. I just thought it was a curiosity. I didn't harvest any, just chewed a leaf now and then. When I went to look for the plant
the next year, I couldn't find anyone selling it. So I did some research on-line. It is quite an interesting story. Apparently it is an acceptable sweetner and commercial crop in many countries. The FDA has banned it in the US for use as a commercial sweetner due to insufficent testing (or to protect the interest of sugar growers). Since it is an herb, it can be purchased as an herbal supplement, since they are not as regulated.
There are books published about this herb and how it can be used to replace sugar in your diet since it has no calories.
Here are a few sites on stevia: Cooking w/ Stevia stevia.net