whitening teeth strips

Ever since Im in U.S., I was bombarded by the various n amazing ads... some many wows,,, n convincing... their tv ads pro (hehhahahah)

Lately, caught my interest is the crest whitening strips. i often see ppl spree on this in spore on U.S.A drugstore. So since im nw at here, i may as well give it a try after reading some gd reviews. Currently, there is 2 quite prominent brands; Listening n Crest. Personally, i feel listening is much into mouthwash pdts, i decided to stick to crest. Crest is nt a brand u heard in spore, n i came to know they recently launched a latest pdt Crest Advanced Seal (in feb 09). It is a big wow compared to it previous version pdt. It solve most of minor flaws, definitely is a "advanced". Cost around usd 30, sound abit pricey. since im abit new to this, i buy its founder pdt (classic; cost abt 18+) from my nearby store.
The product is used by sticking a strip to the teeth and used on upper n lower part. It said to has some minor to moderate effect. It is most effective on yellow teeth. A side effect of Whitestrips is a slight stinging sensation in the gum that may be occasionally piercing. White spots may appear on teeth. For Classic, the strips maybe flimsy compared to Advanced. Apply twice a day for 30mins each, whereas Advanced onli need once per day. I was amazed that this could even apply back to back meaning continuously after one application, u can apply the second one (if u wan a faster results??) It is advertised to whiten teeth within 2 weeks. Conversely if u use it for a mth, the effect can last up to a year. Advanced is even amazing, said to seen results almost instantly?