For those who enjoyed this, Eeben Barlow (one of the first South Africans who eventually formed Executive Outcomes, one of the most famous PMCs) had written a book also titled Executive Outcomes that was long out of print but is now available for download on Kindle. It's about 300 pages too long but is a really fascinating look at his side of the story and is damning for international groups who responded to crises across Africa but did little (read UN intervention in Sierra Leone) or were outright harmful.
For a book pointing more forward, than looking back, I recommend
"The Modern Mercenary: Private Armies and What They Mean for World Order"
by Shawn McFate.
Could probably use an update post Afghanistan / Syria etc.
I know, it's an obscene price given the category of the book but I guess he's got a very small niche of people who are willing to pay a lot for his tell all. I personally found it worth it (for the digital one of course)