User blog comment:Krufix/Armor/Magic pen is anti health stacking./@comment-5284325-20130723124329

Your examples with the cost efficency of chain vest compared to Giant Belt/Warmg's are a bit misleading because you assume the target has 0 armor. if the target would have had more armor they would rather buy health.

Anyway I think flat penetration is most effective against anyone with low resists, not just people who stack health (which is pretty stuped and inefficent anyway)