I am currently running around with a lvl 18 demon MM, and the whip attacks are very useful for finishing off opponents in a hurry if your demons get into bother.
The one annoying thing I have found is that the demons get very close up behind you, especially the larger ones, which means you have to be creative with the angles you need to select an opponent, which often means you need to extricate your minions from multiple opponents, hence why the whip is a great weapon to have up your sleeve.
I have the leadership buffs which also help greatly.
