I tried a few sessions of bio-feedback but quit because I got frustrated by it and not being worth the time and money.
During the intake the therapist described Ritalin as "poison". I should have probably gotten up and left right there. If you have the opinion that Ritalin is overprescribed, or that it should not be given to small children, that's all fine with me. But "poison" has a pretty clear definition, you'll find that whenever someone refers to a drug as "poison", you're dealing with pseudo-scientific quackery.
What made me quit was mostly that I couldn't find any correlation between the signals received from the electrodes and my own state of consciousness, be it more relaxed or more concentrated or alpha/beta waved, whatever.
When I watched the graphs on the monitor, I noticed a few things. There is a LOT of noise. If I'd clench my jaw, move a muscle in my neck, my ears, whatever, it'd cause an avalanche of noise, completely drowning out any possible brain signal. Ok so you sit still, you're meant to focus or relax anyhow. Except that muscles just seem to generate a whole lot more electrical signal than your brain, and every time I even blinked my eye there was a burst of noise (probably also because the eye muscle is relatively close to the electrodes). The software did nothing to filter out these noise-bursts, even though it'd have been trivial to make at least a basic attempt that would throw away the data during a burst so the other filters wouldn't trigger.
Ah, the other filters. Well, it quickly became clear I knew a lot more about DSP than this guy. He had no idea how his device operated, at least not how the signals were transformed into whatever was displayed on the screen. There's not really an excuse for this. Sure enough a surgeon might not know about the algorithms used to convert an MRI scan into a picture, but the radiologist does (at least, on some level), which is why we have radiologists.
So you know about these alpha/beta/theta/gamma brain waves right? They're at 12/10/7/3 Hz frequencies or something like that. Now I always had the idea that by this they meant some fundamental Eigen-frequency of signals in the brain, so you'd think to apply some auto-correlation to determine the base frequency and its harmonics. But instead he had a bunch of bandpass filters running concurrently being graphed through some ancient MS-DOS program with obvious leakage from one band to another and we were looking at the raw filtered signal, not even its energy and as I said there was no noise suppression.
I'd have loved to take that device home, write some code for it and see what it could detect though. Hell, even detecting muscle movements is already way cool :)
Anyway, no correspondence between my state of focus or relaxation.
Staring at a computer screen (with a game, usually one frequency band was used to control a game of some sort) for 1-2 hours per week, actively trying to relax or focus would definitely have a result of course.
Which is why I'm doing a universal yoga meditation class. Dunno if it helps with the ADD, but it can't hurt and it definitely has some other advantages (notably: posture and stress/tension). One thing I do notice, yoga works best if I haven't taken meds that day. You'd think it improves focus, but this yoga class is mainly being able to really feel your whole body and muscles should not be tense for that, but on meds I find I get way more fidgety and subconsciously re-tense every muscle I relax as my focus shifts to the next part of my body. Fortunately, noticing and being aware of such subtle effects in your body is exactly what the class it about :-)