The approach this book takes to teaching a language goes against everything you will read about language learning. Entire sections of really dense grammar with no practice material are interspersed with word lists you’re supposed to just memorize. The material in this book is fairly outdated, too. It was written in 2003, and it feels like it was written in 2003. Moreover, there are a lot, and I mean a lot (!) of mistakes and typos all throughout the book, so I hope you weren’t going to trust it, because you absolutely shouldn’t.
Do yourself a favor and buy the new edition of Suomen Mestari and Harjoitus Tekee Mestarin. It won’t be written in a British-centric context like this book, but arguably it shouldn’t be anyway.