My teeth were fairly yellow from red wine and coffee so I had Brite Smile done about 4 years ago.
I am surprised to see how many people have had pain (my step-daughter had to have them stop the procedure, but I'm not sure she was using Brite Smile). I had no pain. It was done in my dentist's office and took several hours as I recall, maybe 3. Afterwards, I was given a tray and whitener (Sapphire) to use at home as needed. The first year I didn't whiten. Now I use the tray about 1-2 days a month. My teeth are very white.
I am very satisfied with Brite Smile and wouldn't hesitate to do it again when I need it. My dentist is thinking of changing to Zoom. I don't know anything about it but I wonder why he would change from something that worked so well for me.