So, are Bloodspeakers really worth using?

I started playing a Valkia campaign, haven't played any flavor of Khorne campaign since picking up OoD. I'm just wondering... are Bloodspeakers really worth using over a Chaos Lord of Khorne? They have the stats of a Sorcerer Lord but their "Khornate spells" are significantly worse than regular spells. The best buff they get also comes with a huge debuff, and their relatively weak heal damages them... not exactly a fair equivalent of actual spells. Arch Lectors seem far superior in comparison.

Also, the Chaos Lord of Khorne just looks way cooler. So why should I use these guys?