I agree with Molly -- braces can be really hard on the mouth, especially if one has Amalgam fillings, so OP will counteract that.
And I have to compliment you on your enlightened son! It would be great if he started a new OP trend among teenagers...I bet girls would love it for the cosmetic effects alone (tooth-whitening and skin-clearing). It's so great that your son can start thinking along wellness lines at an age when so many kids are starting to think along self-destructive ones. He'll be glad he did when he's 40 and everyone else is getting root canals like crazy, and he has got strong, healthy teeth in a healthy mouth.