I've been reading this book for the past four years, and it has certainly shaped how I identify different personalities.
While it's true that there are likely thousands of unique personalities since everyone is different, this book simplifies it in an accessible way. Simple is better than complex.
I recommend approaching it with an open mind. When I first read it, I initially resisted some of the ideas, but over time, my perspective shifted, and I now find it incredibly helpful. In the workplace, this book helps you recognize different personalities more easily and gives you techniques to better understand people, which translates into improving how you interact with various personalities effortlessly.