laser whitening is done once and thats it, you could end up looking like a bee-gee and look ridiculous depending how dark your tan is, if you drink coffee, red wine or smoke, they will start to stain unless you use a decent toothpaste, but its not a permanent thing.
there is also the home bleaching kit, the dentist will make a set of silicone gum shields for you, you are given 4 tubes of bleach gel, place a drop in the shield on which teeth you are doing, leave in over night and brush in the morning. this also softens plaque.
the home kite you can basically do as and when you want, and just rebuy the gels.