It works, but you need to prepare. It can cause EXTREME sensitivity..most dentists recommend that you begin using a "sensitive" toothpaste well in advance of the procedure.
Have you tried Crest Whitestrips? They are quite effective and while they can cause some sensitivity, it's nothing like Zoom can cause! And, it's cheap! Under $50 will do a nice job! No tooth whitening will work on false teeth or crowns.