Pokemon Sword and Shield: The Official Galar Region Pokedex
No, it doesn't. I have emailed The Pokemon compnay asking if they were putting out guides for the expansions too, they said to stay tuned to the channel for any news on that front. So far no news about it.
It depends on what you want, but yes; there are very real differences in the books. The Pokedex details each of the Galar Pokémon. Move sets, evolutions, etc. The strategy guide is a guide to how to beat and the little secrets in the game, including things such as maps and recommendations. If you need help with or want more info on the game itself, get the guide. If you want to learn more about the Pokémon, get the Pokedex.