I think any guidebook is better than none. I like to know the details about places I am going and
Brierley's book is sufficient for that. I am not a fan of the "not to scale" maps and the elevation scales that are not very accurate. I like to prepare somewhat for the day ahead so I can make some decisions about a detour if I want to take one to visit a monastery....tried that today, went right when I should have went left....
Oh well, I am enjoying Santo Domingo de Calzada a lot!
It all depends on what the camino is going to be for you. If it's a spiritual/religious thing, you might want a guidebook (
Brierley's fits nicely in my pants pocket on my right leg). If you are just out to do a walk, don't care to know about the history, then don't get a guidebook, follow the yellow arrows, or get one of the sheets from SJPdP Pilgrim office.
Up until today, I have seen very few signs in English at the historical sites, so if that's important, a guidebook would help explain basic historical stuff.