O_o I haven't seen the 'volume 1' on either cover. Then again, I may not have looked close enough.
There will be two guides, like with all previous games. I've always found that the Nintendo Guide, versus the Prima guide, has more accurate info. Better Pokedex, too.
The only way I'd tell you to buy the Prima guide is if you really wanted a poster, since all their guides seem to come with one.