In the article "Read this before paying $100s for neurofeedback therapy" the author points out a number of reasons to be skeptical about alpha biofeedback.
I do think there are a surprising number of not so well informed practitioners out there providing neurofeedback with little knowledge or sense of scientific discipline, and in some cases bordering on outright charlatanism. So there is definitely a case for skepticism.
But I would add a couple of points. The initial research cited, from the 80s and 90s, is quite a long ways from modern biofeedback. Personal computers with the necessary speed and processing ability, software, equipment, and protocols had not been developed at that time. It was after that time period that EEG biofeedback exploded.
The article seems to focus a bit more on alpha biofeedback than biofeedback targeted to specific anomalies (although ADHD is mentioned). In some ways it is easy to slough off the alpha training of the sixties as hippie nonsense. My take would be that alpha training, in general, is akin to meditation. And if you don't go about meditation in the right way *, for example, you could spend decades and not attain stream entry, i.e. in some way be wasting your time. Off the top of my head I can point to the addiction rehab studies of Peniston and later Scott as examples of successful alpha-theta training.
However, overall the article does have a balance to it, and I would agree generally with the skeptical attitude. The problem is when skepticism becomes knee jerk. I am reminded of an old researcher who commented on Tibetan monks meditating, and expressed the opinion that they were simply wasting their time.
I can say that EEG biofeedback definitely helped me, but for my particular set of conditions I suspect proper meditation would have done about the same thing. For certain disorders, I think EEG biofeedback does have the ability to produce miraculous results. Hopefully more and better research will point the way.
* One proven way, The practical meditation instructions of Mahasi Sayadaw (~40 minutes mp3).