Is zoom whitening really effective? He recommends the take-home trays. But a friend said her teeth were at least 3 shades whiter after the treatment, and I could tell they were whiter. I tend to trust my dentist, but I did like my friends results..

Personal preference. Zoom! Will do about same amount of whitening that 2-3 weeks of home whitening can in 1 hour. Take home whitening kits are less expensive. The biggest difference is convenience. In a "i want it now" world, zoom! Is popular because of the results are achieved in 1 hour. As a business man, I would prefer home kits too. Reasoning is chair time and they cost me a lot less than zoom!
YES, YES. Zoom professional whitening is very effective, however, the trays your dentist recommends will work also it will just take a little longer. Both will give you great results!
Yes very. Zoom whitening is a very effective method, because you get a drastic results in less than an hour normally and it is safe as you flow the dos and donts right after treatment, trays work too, they only take longer to reach the desired results. They can be used after the zoom to mentain and for touch ups.
Both works. Both take home and zoom ar effective. It takes few weeks for take home to achieve the same result as zoom.
Teeth whitening. Every individual's teeth whiten differently. Your teeth may whiten less or more than your friends even when same method is used. Keeping that in mind, zoom may or may not work better. Zoom has a higher concentration of hydrogen peroxide than most take home. But if your dentist gave you same concentration of bleaching gel, it should generally have the same effect as zoom if you follow directions.
In. In my experience, instant whitening products like zoom work great but not better than at home whitening. The advantage you get with zoom is it takes one appointment. At home whitening takes many days. If you don't have wedding photos tomorrow or your 20th class reunion, maybe consider the take-home trays and save a few bucks. What you save in money, you pay in time with whitening. If you have the time and you think you will be diligent, follow your dentist's recommendation and do the take-home trays.