My main problem with that book is that it seriously lacks organization, in addition to a set of well-defined and potent principles. As you must have noticed, they tend to give you a series of problems and just explain them away. They TRY to make it seem as though it were clarifying their main principles, but it simply pales in comparison to books like The Logical Reasoning Bible / The Logic Games Bible. The way they've organized that book seems to me like a bad essay with weak content that, despite an attempt at seemingly convincing structure, ends up as poor.
It won't hurt you seriously, but there are books out there that are incomparably better.