As ANARIE has said, Truvia and PureVia are basically artificial sweeteners. You don't find these forms of stevia in nature.
This link gives more: www.sparkpeople.com/resource/nutrition_art
These type artificial sweeteners are not good for you...for they provide nutritional benefit for your body.
These type artifical sweeteners are not bad for you, for studies have shown them to be safe.
So the question is do they benefit your weight loss plan. Are you in need of an artifical sweetener to cut sugar calories from your diet...If so, then they may be of benefit.