Use the targeted adjustment tool instead of dragging the sliders. Drag up to lighten an area's rendition in b&w, down to darken it. Instead of continually glancing back and forth between image and sliders, you keep your eye on the picture and how tonal areas are being rendered in b&w.
I find the targeted ajustment tool less reliable for fine ajustments.
That review is dead-on IMHO. The Diallo book is very basic; it tries to cover everything remotely related to B/W photography, but ends up being only a very broad overview with no real depth on any topic. It is very much a "beginners" book IMHO, and should not have "Mastering" in the title. I bought this book when it first came out based on all the glowing reviews, and was very disappointed. I wish I had seen some reviews like the one above, it would have saved me some money.
I find your comment about why would Amazon allow such a review puzzling. Amazon doesn't censor negative reviews (unless they break rules regarding profanity or such), and why would they? It wouldn't be a very useful review system if they only allowed positive reviews. They have a voting system where people can register whether they consider a review helpful or not (and BTW that particular review has been rated quite positively).
I'm afraid I argree, the title gives the impression that the reader will be able to master digital black and white, in truth theres very little on the actual B+W conversion process, with chapters on portfolios, building a digital darkroom, and digital capture, the book tries to be "all things digital" IMHO.