I like the concept. I’m just not sure how flat other keys (or whatever goodies you carry with your keys) will lie once they’re connected to the split ring. Will you wind up with a spiky mine-shaped mess in your pocket, or will it be more subtle? It probably depends on the diameter of the key holes of the keys on the ring relative to the diameter of the split ring, but that’s getting too analytical, even for me.
The key blank can be cut by any key cutter to fit Schlage SC1 or Kwikset KW1 keyways. It runs $7 for a pack of two.
Split Ring Key [Amron Experimental]