I use this with molds made by my dentist.
Initially I purchased nite-white thru my dentist, but he sold at a price almost 4 times more than I can get it on the web (it discounts 75% or so if you really shop).
I drink coffee by the gallon, and have teeth that are susceptible to staining.
Using nite white for 1 hour, on consecutive days, gets the teeth as white as can be. That doesn't mean pure white teeth for everyone, because some teeth are naturally brighter white than others.
I do my teeth every 3 months, or whenever I think they need it.
It really works as advertised, and is safe when properly used. READ THE INSTRUCTIONS. Use only the tiniest drop for each tooth (the package shows the actual size drop you should use). Using too much is not a smart thing - don't even try it.