I have used the crest whitestrips and had great results, I used the one that does it in 7 days but ended up taking 10 days for me because after the first few days I couldnt put them on my teeth twice a day like your supposed to because of the sensitivity factor so I spread it out to 1 time a day for the last few days. It wasn't to unbearable but I have very sensitive teeth in the first place so it was just enough to make me slow down on the use a bit, but if you don't have overly sensitive teeth you should be ok.
I use a whitening toothpaste like colgate ot whatever to maintain the work I did on my teeth, I am also a fellow tea drinker so you could say I am addicted to whitening toothpastes to help keep my teeth nice looking.... good luck