So are you meant to use the wargear in the errata or from your codex?
I paid £20 for this book and because of this I get cheaper wargear for my flier. I wonder if they will FAQ the BA and GK codex to lower the points costs to what's in the errata.
There are actual rules for wargear in the Compendium and it looks to be about the same honestly (Grey Knights and Blood Angels still have to take their respective missile options, and Grey Knights still get Fortitude, ect).
As for points cost for BA the only things that got cheaper where the locator beacon (by 5 points) and the Extra Armour (by 10 points). Grey Knights follow suit on the wargear, but the codex specific stuff (Truesilver Hull, Psybolts, ect) still costs whatever they cost in the codex.
Honestly I'm not seeing much here that really says "you NEED this book", more "if you want it, it's here, and there are a couple small perks for having it that rarely matter".