I'm not sure why Cleverley gets brought in for comparison. Two totally different players in my view. Cleverley shits on Fellaini for creativity / vision / passing ability, but Fellaini brings a whole load of other attributes that aren't tom's game.
They're both CM's and there are two CM spots at United. Though he's obviously nothing like Cleverley in style, they'd certainly compete for position and hence the comparison.