I bought this book when my baby was about 3 months old and not settling into any kind of routine I had tried with her, waking up quite a lot during the night etc etc... Initially I tried to stick rigidly to the routines and the methods Tizzie goes through in the book, but still found baby could not wait until the set time in the routine to feed, would not self settle and did not sleep through the night... UNTIL: I started weaning at 4 months on the advice from Tizzie. This was a revelation and I have since been able to follow (although not to the exact letter) the routine for my baby's age, she has been satisfied, rarely cries, self settles at daytime sleep times and sleeps nearly 12 hours through the night. I don't think I would have started her on a routine as early as Tizzie advises (a matter of a couple of weeks old), but if you have been feeing on demand and waiting for your baby to "settle herself into a routine" (like so many people tell you that she eventually will(!) for a couple of months to no avail, then this book points you in the right direction.
In summary, I found the advice interesting, but would say not to worry about following it too rigidly, just use the parts that suit you (and more importantly, suit your baby).