Been using product for 1 month and my teeth are 3 shades lighter according to the colour chart.
Couldn't tell a difference for a couple of days then suddenly the badly stained teeth to the side of my front teeth were almost as white as my front teeth.
Now they are all same shade and nice and white. The powder is good because it doesn't cost a lot and works.
Don't think this powder would work as significantly if you aren't a coffee drinker/smoker so was considering giving 4 stars.. However for me is a definite 5!
Buy this product because it's affordable and a strong competitor for other (ie expensive!) teeth whitening