I play Daemons and I say Yay. A soul grinder with phlegm is only 160 points, it can fire both it's template weapon and it's harvester gun at the same time, it deep strikes, it has 5 str 10 attacks on the charge and has fleet, it's str6 flame template clears infantry out of cover, it's practically impossible for enemy infantry to destroy in assault, it's cheaper than your average daemon prince, and in my experience lives longer too.
If you don't like the model, convert it.
I currently field 2 soul grinder's in my army.
They've earned their points a dozen times over, most of the times i've fielded DP's, they've died to mass bolter or shuriken catapult fire. A lucky lascannon shot has to be LUCKY. Mass small arms fire is pretty much a GARUNTEE.