At over 80 years old, you’re not going to become a grandmaster reading this book. But his logical way of showing how different openings build on each others moves from weak openings to stronger it’s quite accessible and good for the club player.
Middling as a primer, great as a "spot check" for one's overall understanding of the game. This is definitely not the first chess book a beginner should read. For one, at that stage openings don't matter as much as other areas of their game. Too much emphasis on the opening will leave them helpless once the opening is over, and in such instances the one with better overall understanding will win. But I believe studying tricky openings like the Stafford is necessary as there are certain sequences in those openings that you likely wouldn't learn elsewhere. Also, theory has changed since this book was first published. Nowadays titled players (Grandmasters and such) are finding active and interesting tries in openings the author wrote off as "dull". This is with the help of modern engines.
It should be noted that not every opening is given equal attention. Analysis of the classical openings comprise the bulk of this book and sections about the more modern openings like the Sicilian are very, very short. Also, the moves are written in descriptive notation (P-K4 instead of e4), which modern readers might find frustrating to decipher.