Well - its not great. Go to Wiki - its better. Frankly 2 stars are awarded simply because the author took the time to publish a book on a generally poorly covered set of topics.
Indeed other than Pettibone (another poor set of resources in my view) the only book I can strongly recommend regarding the Hungarians is Dr Leo Niehorster's seminal volume - if you can find it for less than a collectors price! There are a few other texts dealing with the Axis allies - and in more depth than this volume.
It is surprising that with the enduring interest and wealth of publications about Operation Barbarossa and the Eastern Front, that there are still large gaps in available knowledge and literature. Post war publications tended to focus on the actions of the German armies, and the key battles they fought in. There was little available from the Soviet perspective and almost nothing covering minor Axis allies, other than passing references (often disparaging) in German oriented histories. The fall of communism and glasnost has led to a trickle of information coming out of Russian archives which talented historians like David Glantz have used to publish thoroughly researched volumes on those same key battles and many lesser known ones, from the Soviet perspective. Very little has been published relating to the actions of the Axis allies (Hungary/Italy/Romania) and/or events on the extreme southern flank of Operation Barbarossa. Partly this is because there are few available primary sources available (most Romanian archives were destroyed towards the end of the war, and there were few biographies published (because most Romanian/Hungarian soldiers were semi-literate at best); partly because there were few German armies (and even fewer elite units) in this zone of operations; and because the decisive actions were occurring further to the north, in the central Ukraine & Poland. Even so, the rapid Soviet occupation of Bessarabia in 1940 was a key decider in Hitler's decision to attack the Soviet Union, and the number of men involved in the far south numbered around a million men, with numbers of aircraft deployed not dissimilar in number to those used in the Battle of Britain. In light of all this Patrick Clouter's book is a welcome addition to the literature on Operation Barbarossa. At 160 pages it is not a large book, but it does pack a lot of information in, presenting a reasonably detailed summary of events, which Axis allied armies were involved and to what extent. There are a number of maps, and a few photographs throughout the book to assist the reader. The author gets around the lack of primary Romanian/Hungarian/Italian resources by using recent publications coming out of Russia as well as the few books available in the English language. He also identifies differences between authors and perspectives where relevant. This is not a book to read if you are looking for anecdotal reminiscences a la Anthony Beevor's books. Neither is it exhaustive. There is still scope for someone to write a more holistic history of Barbarossa in the far south using German & Russian archives and many of the sources listed in this book. However, Three Kings goes a long way to closing what has long been a yawning gap in World War Two Eastern Front literature.