I was packing up the metal Arkham Asylum Batarang I got the other day, and stumbled upon the plastic one. It seemed like a good photo op.
Size-wise, the two are almost identical. From a top down perspective, they are extremely similar. The main difference is on the z axis. The metal one is cut from a flat piece of metal, whereas the plastic one has a number of contours to it.
The center disk is also very different on the metal one.
They are both still really nice, and I can appreciate them individually for their unique and interesting qualities.