Think of it like Lumsden's book on British piston engines. Except it covers both piston and jet engines and in a little more in depth. If your interested in Japanese piston engines it's a must have.
Hopefully it is more accurate than Lumsden's. Numerous times in my roaming around wikipedia, I find errors in engine displacements using the numbers from Lumsden's book.
Japan had nothing like the industry of Europe let alone the US. There is more in this book on Japanese engines than there is in any other book. The sad fact is much of the Japanese records were distroyed during the war and in any event Japanese is not the easiest language to learn. This book covers the subject better than any non Japanese work and probably better than many Japanese works. My copy only cost me $40 or so. A little pricey but it's an esoteric subject and the publisher needs to cover their cost.
I will admit that I was hoping for more but overall I found it to be a worthwhile purchase. If you don't that's fine.