Soooo the true question is: are you going to field a supplement black legion or a regular
csm force from the standard dex?
If you're going for the first you should know some (bad) news about it:
Votlw tax: all the models able to take it MUST take it: the worst from this supplement
imo.
Chosen spam: chosen are troops in a black legion army, they can take 4 special weapons or 5 special
ccw buuuuut so many points... 20 for a naked chosen.... Then add weapons.....then add transport.....meh
Abaddon's chosens: 30 points for an unit of
ws bs 5 termies?! Ahahahahahahah no!!
Special tools: awful... Apart from the skull...
So if you're gonna run this list there are 3 possibilities:
1- you're going for the classic cultist-hellturkey-oblits list (in that case using the supplement doesn't make so much sense)
2- you're going for the bg (handshake and high five, i live for the bg

)
3- you hate so much chaos that you want to lose with them, because you know.... You're gonna lose...
For a classic army i'd suggest you to play what you prefer or one of the list that you can find somewhere in the forum. If you want try also the crimson massacre supplement, is not that bad

(don't you dare taking possessed!) play 'em as black legion and that's all.
Once i saw a good black legion list: it was an average army, its strenght focused on some khorne chosen squads (5
atks on charge)...