I saw this in the chemist yesterday and thought I might give it a try. Having an open mind is the key to constant advancement. It was pretty cheap for $8. This by no means is anything close to a proper scientific experiment but is just a personal subjective opinion.
I did some brief research into how it works and it sounds like it "whitens" by attaching to the tannins that are stuck to your teeth and help removing them off your teeth. Assuming it actually does this, to me, this isn't whitening. It's cleaning.
I think the term "whitening" should only apply to things that actually change the colour of your teeth. You wouldn't call washing your white car to be whitening. It's very misleading.
So the powder is REALLY fine powder. It basically looks like black cornflour! I just picked up the powder with a dry toothbrush and went ahead and brushed my teeth. My whole mouth went black and I instantly felt like an emo.
Because the powder is so fine, I felt like I would easily inhale it. This is a bit unsettling. It is pretty tasteless and doesn't feel grainy at all.
So after I brushed as usual, I spat it out and it looked like the Chinese black sesame dessert! Definitely not as tasty though! It also required a lot more rinsing, to stop people thinking I've become an emo.
I also needed to rinse the sink a lot more and make sure it didn't go everywhere. Luckily it dissolves readily in water!
I would not suggest to use this product exclusively when brushing your teeth as it is just carbon. It doesn't contain any ingredients which have much scientific evidence to keep your teeth and mouth healthy.
My teeth aren't stained much so I don't expect to see much difference but I will try to persevere for 2 weeks and see if there is any subjective difference. Hopefully it doesn't cause any damage too!