I agree with changerofways (though he's tzeentchian....)
I have my 1950 World Eater list posted and so far it has been pretty successful against all armies. i will be in a tournament this sat to really put them through the grinder. I find that the demons are a good small unit to where people ingnore or spend firepower on them that couldve gone somewhere else better. Besides deep strike to an objective in the back field or even just to achieve linebreaker will free up the part of your army that actually does the killing to do what it does best. Both my
FMC have an exalted reward in the hopes to roll the one where you have a chance to spawn more demons by killing enough

Bloodthirster is better by far than demon prince but i have one of each, demon prince becomes a heavy support here so he can capture objectives in the scenario allowing Heavy Supports to capture
And Kharn is a serious killer just stay away from storm shield/thunder hammer terminator squads...he does not have eternal warrior, his only weakness...