Should I get a forgefiend or maulerfiend? Or are they not worth it

I started playing a couple months ago, and I heard a lot of people say that forgefiends were a must have. This was before the codex drop, and I haven’t seen any been used in serious lists. I’m in need of tank busting options, and think they look sick. I just wanted advice for if it’s worth seeking out.

Additionally, what’s the consensus on maulerfiends? Better to just run mutaliths?