If you're already familiar with Jack Bogle's writings, the Bogleheads' Forum, or the other Bogleheads' books like their retirement or investing guide, then you won't need to buy this book as well unless you are a diehard fanatic trying to complete your matched set. Much of what you'll get here is things that you'll find repeated to death elsewhere.
If you're looking for a "how to" investment guide for a beginners, I would recommend you look to one of the Bogleheads' guides - as they're better designed for a step by step process to lay out your investments in the Bogle way.
This to me was more a book on the philosophy of investing - useful little koans to turn to when you need a reminder to stay the course, don't time the market, use low cost index funds, save and invest over time and it will accumulate and grow. Bogle has a pretty standard line of advice, but it's certainly worth coming back to when the market gets screwy and you run into doubts. If you need a book like that on your shelf, this is the book for you. I would buy this over many of the rah rah investing/self help/get rich quick books out there, just pair it with a practical guide.