It looks to me, that this book will be very helpful when walking the おへんろ trail.
The first 42 pages provide general info about the pilgrimage, like overview of the route, public transportation, what to pack and the etiquette at a temple. The information really just on overview, but helps to get a general feeling about the trail.
The rest of the book are 73 detail maps of the trail. They look detailed enough for me, to help to find the right way.
In addition to this book, I read "Tales of a summer henro" from Craig McLachlan, which is a diary from Craig when he walked the trail. Another source of further information about the trail is the JNTO.