If you have seen or see the ad, don't rush out and buy it. You don't need to. Most likely you already have everything you need to clear a blocked drain and keep them draining nicely without having to buy a bottle of something.
Much easier and safer than pouring a chemical down the drain.
I do this once a month in the kitchen, bathrooms and laundry. The drains never block or become sluggish and they don't smell horrible either.
From Debt Free, Cashed Up and Laughing