I have the book and can say it is a basic text based on secondary sources. It does have better maps than you see in a lot of military texts. The quality of the printing does leave much to be desired being faint or smeared in places and the quality of the pictures isn't the best but then again as good as many other bargain books. If you don't know much about the actions in Lithuania or East Prussia the book is fine for the price ($11.50).
There is a very critical review of the book on the Amazon.co.uk site
and the author would probably be wise to try and contact the author of the review and try and get a more systematic list of missed references and review the literature. Createspace is a publish on demand service so it shouldn't be all that much trouble to revise the text. Get a good editor and some knowledgeble reviewers to help improve the product.