i bought some from mercola a year or 2 ago. it was the first time i'd tried kefir and i noticed an increase in energy and feeling of wellbeing.
ive heard its not as good as the natural kefir grains though, so next time i will try and find someone i can trade with.
i put some weight on though when drinking the kefir, over a period of around 3 months, about 1/2-1 stone i guess it was the fat in the milk and i was maybe drinking too much of it (2-3 cups a day most days)
there are websites where you can find people in your area you can buy kefir grains off, i would think this would be better than buying any of the pre packaged stuff, but i certainly noticed an effect from taking rhe body ecology powdered stuff. i cant get raw milk here so used organic pasturised.