For me this book (which I've just finished) has given me 3 insights:
1) Geez, war really does cost a lot. I can't see how any politician in his / her right mind would ever commit their country to such an economy-destroyer. The US and UK are shown to have cunningly tried to both disregard and hide the costs of invading Iraq, and to a lesser extent, Afghanistan, to a shockingly immoral and callous extent. You won't be surprised to know the Iraqis haven't exactly done well out of the war either. Unless you're a defence contractor, war just isn't worth it.
2) Politicians will go to extreme lengths for their own short term gain, at almost any cost. It really is depressing, reading that the US army employs so many contractors to keep the army fatality numbers lower, but at such a cost that they don't give their own troops proper equipment or reasonable medical care after injury or PTSD. That's material cost. The authors also include goodwill towards America and Britain - this book is very well thought out.
3) Politicians again I'm afraid: The Bush administration has managed to hump much of the costs onto the next generations in the form of interest payments, without anyone (apart from the authors) really noticing. This is really quite serious and I winced as I read what services might have to be cut so that this war can be paid off.
The facts and figures are presented clearly and give no doubt that the proper research and reasonable methods / assumptions have been made by the authors, who I must thank for this book. I can't think of any adult who shouldn't read this. The headline figures are very interesting but the book provides more than that; it gave me an education into the non-military effects of war, and how devastating they invariably are.