Unique passives, i don't get it

So this is pretty easy question, how do unique passives work with stuff like and ? Like is it that i can't build two of the same item? or that if i build both of these items i only get one of the +10% bonus to heals and shields? If it's the later of the two, can we maybe get something so that supports who's "thing" is healing/shielding can build more items for that purpose instead of having to build a lot of AP to make their abilities better.