I cannot comment on the effectiveness of n2guard but I would not consider it "pure"
I briefly scanned the label...
Yellow 5 & 6 should never be found in high quality supplements.
I personally take Vit-D, Magnesium, and Zinc.
Vitamin D = 100 ius (extremely small amount for anyone interested in vit-d)
Magnesium and Zinc are in the "Oxide" form. As far as bioavability, I would opt for a different form.