No, I'm not. In order for the ability to trigger, its 6 X barbarian level. Not 6+con X barbarian level. THAT is the problem. That means you have to be at 60 HP at level 10. If you dont want to admit it sucks, whatever, but dont act like I'm trying to present false information. It kicks in when you're close to dead. In order to use it from the beginning of a combat, you need to be going in with your pants down, as opposed to rage, which is good all the time.
Assuming a level 20 barbarian with a 22 con (easily obtainable) and improved toughness, he's got about 276 HP. His berserker strength kicks in at 120 HP, a time when the fight should be practically over, the barbarian should be getting a heal spell from the cleric, or the party should be running. He pretty much shouldnt be thinking about sticking around to make a full attack (and receive one in turn). His benefit is in effect for fewer rounds than rage would be. Its just too situational. All its good for is blowing through hordes of low damage weenies (who arent a threat to begin with).