This is an old book. The content is a bit dated and the message is still relevant. I'd say it's only an introduction to usability testing. I agree that the software industry still doesn't do enough usability testing and there is a lot to benefit. I think the book doesn't talk enough (if at all) about balancing competing priorities in design and work. It is much harder than deciding on button shape.
The book is light and short, and I think is suitable for non-technical people.