I had zoom whitening about 3 years ago and I don't recommend it.
My dentist took great care to start me on special toothpaste a couple weeks prior to the treatment. This was supposed to reduce the pain. It didn't! One second during the zoom procedure I was comfortable and the next second I was in severe pain. They had to stop the procedure immediately.
The pain is like a bolt of lightening zinging through your teeth. It literally brought me to my knees. I was supposed to return to work that day and I had to go home. If I opened my mouth to talk, the room air made the pain worse. It took a couple weeks to calm down.
My teeth were a little whiter I guess, but they were pretty white to begin with. I was stupid to do it. For me, the teeth whitening strips from the store work just a good. Less money. No pain. :)