back sweetening with stevia

Guy at the local brew supply shop recommended back sweetening with stevia. He sold me 10 grams in powder form. He said that 2 teaspoons is enough to sweeten five gallons of cider. Anyone care to weigh in on this? I've planned on making half of my cider sweet sparkling and the other half dry or lightly sweetened sparkling. Planned on bottle priming with table sugar for carbonation into Sam Adams bottles.

As with anything else like this, I think you're best off making a solution of stevia with a known concentration, then make a few couple ounce glasses with varying amounts of your sweetening solution. This should give you a handle on where you like the sweetness level, then you can scale it up to the entire batch's volume.