For the sake of completeness: this is the guidebook I used for my visit to Wales. I didn’t really use it for its theoretical function — information about walking the coast path — but the places I was going were all along that part of the coast, so it seemed like a good book to buy for information about places to stay and other practicalities. For which purposes it was fairly helpful.
If you were walking the coast path, I’m sure it would be a bit more helpful still, although actually the path was generally so well signposted, and the route is so self-explanatory (follow the coast!) that it’s probably less important to have a specialised book than it might be if you were walking, say, the Pennine Way.