I have read Volume 1 and 2 when I used http://mangatakeout.com/ website.
It is actually not a graphical manga as there are no illustrations.
This book made me laugh a lot. The story was very captivating even given the fact that I saw anime prior to reading the book.
As far as actual story: there is secret miltary for hire organization that represents good guys. There are bad guys that use similar high tech. Main characters are teenagers with a bit of romance. There is a lot of tactical action and laughable moments due to nature of characters.
The book author said that he wanted to write a book that is easily translateable into anime. The actual anime follows the book very closely. Both are a lot of fun.