User blog comment:Krufix/Armor/Magic pen is anti health stacking./@comment-6000413-20130724165943

I agree with you and I consider early flat penetration an extremely powerful tool, in particular against health stackers that don't stack resistances. I still have to decide if %penetration is just as efficient: it's true that when the enemy has high armor it becomes really useful, but most times you should aim the most squishy dps champions and they probably won't have enough reistances to make %penetration as effective as flat penetration.

Of course, If a champion can apply multiple stacks of BC at the same time or/and to the whole team, that's great, but I find it should be built by some bruiser or jungler.