Oh it doesn't appear to do the half press to focus thing. I don't think that iPhone button even has a half press mode. You still have to tap the screen to focus, but at least you can press the button to activate the "shutter".
That's good enough for me. If I'm not walking around with a full DSLR kit, I often have a compact mirrorless with me. The iPhone is for quick and sudden shots and I'm not worried about it being perfect.