As a smoker and coffee drinker, I know what it's like to wish my teeth were pearly white. Well, they may never be THAT white again, but this product definitely exceeds expectations. I first bought a pen two months ago, and after only two days' application, my teeth looked awesome -- like I'd just had them cleaned. The instructions say you can use the pen 14 days in a row, but I think I stopped after four days because I was pleased with the results (and lazy).
Two months later, I decided to try it again and see what would happen if I really did use the pen for 14 days. I'm three days in and my teeth are already sparkly. My teeth are generally very sensitive, but the pen hasn't made that worse at all -- there's no discomfort and no increased sensitivity. I love this product.
It IS a bit of false advertising to say that you can use the pen at the office and on the go. The gel looks kinda smeary and, well, gel-like on your teeth, so it's really not the sort of thing you'd want anyone but your nearest and dearest to have to look at. But it's extremely convenient and absolutely does what it promises to do.