I have done the Japanese straightening treatment and also the Brazilian Keratin. I did not like either one. I have fine, wavy hair, though a great amount of hair, and both treatments made my hair so flat that I looked as if my face were huge and fat and my hair was flat against it, thinning out on the back crown area. It looked like greasy, unwashed hair, even though I washed it every couple of days. It also damaged my hair. I could easily tell where the line was of the new growth versus the treated hair because the treated hair had split ends everywhere. It took years to grow out since I have very long hair, and will never do it again.
I should have known something was up when I saw they were using the same product on me as they were using on some ladies with very kinky, ethnic, thick hair. I feel that they used a high strength on me when I didn't need it. I was very clear that I just wanted to get rid of frizz which is constant living in a humid client like South Florida, but I did not want to give up volume and wanted something that would not be too harsh on my already dyed hair.
Many stylists will tell you that anything containing chemicals will dry out your hair and that the ones who claim it's actually healthy and revitalizing are just hoping to make a quick buck. I feel that's pretty accurate. I would not mind a deep conditioning treatment but anything containing formaldehyde or other strong chemicals is a no-go. Putting dye in my hair is as far as I am willing to go in terms of chemicals at this point.