In my humble opinion, if such a book happens, it should have 3 parts :
1) the scientific basis of brain entrainment, history an so on,
2) report of a study conducted by... (University of...) on a sample of n.. people (students / businessmen / social workers / whatever) using BrainEv, that gave these results .... and ... and ...
Based on this study, the proven benefits of BrainEv can be described as... and ...
3) testimonials
I think the value of testimonials is to illustrate, personalize, help readers to relate to their own experience and needs, but first you have to convince with factual, scientific basis.
Testimonials alone could give the feeling that BrainEv is a method with a good placebo effect... which I'm sure it is not (I like to think that, so the placebo effect works better for me

...).
I litle less ambitious version could be a good report in a magazine about psychology or wellness or neuroscience...
