It starts out great. It really brings home the idea that very few if any business practices are ever really tests. People make assumptions that not only they never question, but that eventually become part of established business literature.
Then it slowly devolves into your standard blah blah business text where the points are so vague, or contradictory, as to make the book not that worthwhile.
But the essentially point is good. If you want to know if something is working, test it.