The book is a nice intro to the DISC concept. But for that it felt too long. There are a lot of ideas how to use DISC, but most of them stay really on the surface and just repeat the concept over and over.
Another aspect I didn't like that much, it feels like the authors bring DISC as a single standing concept, which feels really strange to me. Looking just through DISC categories people are stereotyped and the next people problem is probably just around the corner. I would have wished, that the others acknowledged more the limits of the DISC concept and give a hint on other strategies and techniques to accompany DISC.
So, a good intro to DISC, a relatively short read and especially the beginning with the 2 questions assessment is very good. But probably there is better material out there.