A child may HAVE ADHD, but it is not what they ARE. Never tell a child they ARE ADHD.
Dr. Amen, who wrote the book "Healing ADHD" claims that it is useful. He has done a LOT of research on ADHD. (His book is really impressive, if you haven't already read it.)
We haven't tried this. Vision therapy seems to be the biggest help right now for my son (he had to move to stop seeing things double.) If your insurance would pay for the neurofeedback, and you have the time, it might be worth trying to see if works for your child. As previous poster said, it may not have long term effect, so you may need to ask about exercises that can be done at home without the equipment. (The equipment is needed at first, but once the person learns how to alter the body responses it is not needed, at least that is my understanding of the process.)
I think that like vision therapy this is not a cure all and will not work for every person, but that doesn't mean it won't work for some people. The only way you will know is if you try.