I've installed that component and though I really like the idea, I find that it's a bit to powerful. I've been noticing that it makes archers/ranged weapons pretty much useless in the game. Even firing on characters with leather armour I gets all sorts of "character immune" messages. What I've done instead in my game is reduce the modifier to one below the armour class, then added a maximum percentage based on armour weight. So heavy armour has a 90% probability of the effect working, leaving a 10% opportunity for my ranged weapons to do some damage. Light armour I've set at 70% probability of the effect working. I haven't tried it in a game yet, I just thought I'd pass the idea along.
Another thing, it doesn't make sense to me that shields have damage reduction. The whole purpose of them is just to deflect blows, not prevent damage. That's the armour's purpose: you get hit and the armour will absorb some of the impact, or deflect a sharp edge. Shields on the other hand don't do anything towards reducing damage otherthan stoping a weapon from hittingyou in the first place. For that purpose, regular armour class is sufficient.