I run two food blogs, one focused mainly on Japanese cooking, the other just on bento lunches. (I'm Japanese but live outside of Japan.) I finally got around to taking a look at this book.
The pros: it's a nice visual introduction to fairly traditional bento lunch boxes. (Keep in mind that 'bento' can be something other than a portable lunch.) The presentation is very attractive.
The cons: even as someone familiar with the ingredients and cooking methods I thought that this book looked rather intimidating, because just about every single recipe calls for ingredients that are only available from Japanese groceries. Actually quite a lot of the recipes call for ingredientat that would be very hard to get outside of Japan. Clearly this is a translation of a Japanese bento book, and no consideration is given at all to how available certain ingredients may be or not. (This is something I always try to keep in mind on my sites.)
The presentation feels just a bit outdated to me. Current bento books in Japan have a much simpler, modern feel. The instructions are also rather abbreviated, as if the intended audience is the fairly experienced Japanese cook (which it probably was when it was written originally).
So, I think for most people who don't live in Japan this would be a nice picture book to have around, perhaps as inspiration and eye candy, but perhaps not too useful for everyday lunch making for a typical American.