I tend to like supplements by nature made because they are known for their quality. If the bottle has the USP marked on it I'm sold! And this brand tends to have that label. I like to look out for the USP labels because it means the company has submitted their own product to be tested for its quality. This is great since the FDA doesn't regulate supplements or vitamins.
Whenever I start feeling sick I pop a couple of these and drink a lot of water. Since using it, I've warded off a lot of sicknesses. I can't say it works every time, but I would recommend it for anyway who feels like they might be getting sick.