I have some yellowing of the teeth from being a daily coffee drinker, after several uses, there is a noticeable difference. Its a vwry easy to use product, just follow the instructions included in package. If you have sensitive teeth, i would recommend that you dont use it as frequently as recommended. The results should last a significant amount of time.
I would rebuy if needed, but i do need to be more cautious as i have sensitive teeth, and like all whitening products, it will make your teeth more sensitive