what's the difference between "protector" shields and "reinforced" shields?

I understand that reinforced shields state that they take "half" the damage, but I am just confused on why won't that be so much better than regular shields. And why are reinforced shields one long bar/slot instead of 2 slots like a regular shield? Also I am talking about v1 shields, I am not at the point in the game where I have gotten blue(v2) reinforced shields, if they even exist.