I admit it. I'm not an airplane or tank buff. I think they're somewhat interesting, but I definitely don't speak "tech-ese" or have dozens of models hung in my room. However, my interest was piqued by these two books. At first, the concept of randomly selecting two types of airplane or tank and talking about what would happen if they "dueled" each other struck me as slightly boring, but I was very, very wrong. Not only were the varieties of war machine not randomly selected (they complemented each other very nicely and were apparently each other's worst enemy in both cases), the books cover much more than a simple "duel." They talk about the history, mechanics, and design of each machine in-depth, and cite specific examples of both fighting each other. These books are each totally stand-alone and can be read for fun. Or, if you choose, they would work nicely as part of a larger unit study (even though they aren't specifically designed for homeschoolers). Along those same lines, Osprey also publishes books on how to create models of each of the machines described.
The books seem to be designed for high schoolers and adults. Despite the heavily technical language, even those who aren't fluent in the language of "V-1710-39 engines," etc., can benefit from these books. Compensating for the lack of easy readability are the wonderful illustrations dispersed throughout the book, ranging from schematics of tank machine guns to a view inside the cockpit of a P-51 Mustang. In each book is a beautiful two-page spread portraying the two "combatants" in the heat of battle. These books really appeal to the visual learner. They could be effectively used for some in-depth military equipment research.
As mentioned, the language is very technical. It is assumed that the reader already knows the difference between 88mms and 17-pounders. And the books are a tad on the expensive side. Suggested retail price is $17.95 for each, but they could probably be found for less. That being said, however, I think these books do a superb job of tying the content to the historical context. They feature maps of troop movements, stories of specific combats, profiles of famous aces, etc. I would highly recommend them for military enthusiasts, but they also would be a great addition to unit studies or history studies.