Why pay hundreds of dollars to whiten your teeth when you can pay 20 bucks to do so? Assuming you're teeth aren't extremely discolored, these work great! I've been using them for the last 3-4 years about every 6 months or so. I prefer the 7 day cycle. ( 30 days was way too long and I never tried the 3 day). People are always asking me if I get my teeth whitened. I'm telling you, these do the job...So much so that when I went to have my teeth professionally whitened last year @ Brite Smile, ( I don't know what I was looking for...I wanted gleaming, chicklets gum, Alicia Keys kinda white!! ) the dentist told me my teeth where whiter than their whitest shade!