how the forget do you use that slow piece of stuff
It's like a point and click adventure game, move your cursor over the enemy, time your windup as he's running at you, kerpow, his head is in fragments at your feet and his lifeless body crumpled. Then shout at it just to be sure he's dead.
Edit: I'm probably the guy who most people hate in online games. If I find something ridiculously "cheap" I have a blast using it. I discovered Commando pro + Marathon pro + Lightweight pro with a tac knife on MW2 on launch day and the act of being too fast to shoot and knife lunging at people from 100 feet away was hilarious and entertained me for years.