I read it when I had my first baby. The thing I disagreed with most was listening to my 6 week old baby cry her heart out while I patted her for the minimum 22 minutes Tizzie says. It didn't feel right for me and I needed to pick her up to settle her. I also didn't agree with waking my sleeping baby according to the clock/a routine written in a book. My feeling is that DD is a human being, not a robot so if she needs a longer nap she can have one.
I ended up reading a few other books and settling techniques and used all the information to do what I thought was right/what worked for DD. I followed SOS routines loosely.
Interestingly, when DD was 4 months old and still catnapping I new I needed to ditch the dummy as SOS and other books had recommended. So at that point, when DD was that little bit older and I was extremely over tired, I was able to let DD cry for certain periods and then pick her up and hold her/comfort her and repeat until she learnt to sleep without the dummy. It was still hard to do then but I just couldn't do it like Tizzie says when she was 6 weeks old.
So my advice would be to try it and if it works and you are happy then great, and if not, understand that Tizzie does NOT have all the answers and there are lots of other great methods out there. All the best