What in essence is explained here is that there are different tax systems in different countries.
Next is explained how to move from country A to country B. This is a fundamental human right, and one of the founding principles of the EU. This is therefore 100% legal.
This book strongly advocated against “black hat” tactics (these are not needed), and doesn’t include tips on hiding from the tax authorities. If that is what you want don’t buy this book or email me.
On a final note: this is an overview of how the international tax system works and not specialized tax or legal advice for your unique situation.