You should try a search...use the google.com advanced search feature with longhaircareforum.com as the website because the LHCF search engine is non-existent. I am pretty sure this has been discussed before...
My .02 I only think a product is natural if I can eat it and not have to call the poision control center.
Yea, it may not taste good and yea it might give my tummy an ache but if I can eat it then I figure it's okay. NOW, given all the junk food that we eat with all the chemicals in it, this might not be a good brightline but it works for me.
My feelings are that either this is a relaxer and has chemicals in it at which point it is NOT natural OR it is completely natural and the results will probably be similar to using henna (meaning they don't last after a wash).
ETA: The fact that you have to/can wash your hair before applying it would also lead me to believe it is a natural relaxer.