I've been using erythritol for a couple of years now as a beverage sweetener substitute for sugar. This isn't nearly as sweet as sugar, but since it's zero calories and zero glycemic index, it's well worth it, I think. I would rate the erythritol itself 4 starts.
I've ordered from iHerb.com several times and been satisfied. However, the last order I received is full of solid lumps. (Hence I'm rating the overall experience with iHerb.com+erythritol as 3 stars.) I can probably crush these into a usable powder, but it's going to be a big pain to do this. If my next order arrives "lumpy", I'll order elsewhere.