I used the 11th Hour CISSP Guide as a companion to Eric Conrad's "CISSP Study Guide". I used it in the days leading up to the exam. It's value to me was the distallation of the salient points of the CBK. As you reaed the short and concise text, it helped me as I read topics within each domail to say "I know this topic or I don't know it well enough". So it was a good yardstick against which to measure your knowledge on the days prior to the exam.
I can't say I would use this as my only study guide as you do need a more in depth grounding in the domains, but this book certainly served its purpose on focussing my energies on the areas which I needed to hone in on prior to the exam.
By the way, I used Conrad's CISSP Study Guide (the bigger book) as ny priciple study guide for the CISSP exam and the GIAC exam and I can honestly say that text as well as the 11th hour guide were instrumental in passing both exams the first time. Compared to three other major texts (Krutz/Vines, Harris, and the official ISC2 texts), Conrad's book distills the CBK into real world, stuff-you-can-read prose. Definitely recommended as they helped me pass the first time.