Managing the rule isn't so bad, but what gets me is the fluff behind the unit. Demo corps, the great bears, and whatever else that has backswing are supposed to be the elite troops in a melee fight. Doom reavers are screaming angry psychopaths who can't tell friend from foe once they get going, and that makes complete sense.
The great bears have precision strike, allowing them to cripple jack systems almost at will. But that one time you wreck it on the first swing "Omg I can't stop" he spins around like a top and cleaves his comrade in half. On top of that they have defensive line, which means in many situations they want to stand shoulder to shoulder.
It probably won't have a major effect on any games if you space the bears correctly, but I know eventually there is going to be that one time I need that other great bear to attack something and WHOOPS I just killed it.