I saw the article for this, and my first impression is that I was surprised that something like this didn't already exist. But alas, there is a company called Yellow Jacket that has developed a stun gun attachment for the iPhone that can "can shoot 650,000 volts of electricity into a would-be predator (or unfortunate butt-dialer?) for just $149."
A few thoughts:
A) $149 seems like a reasonable price. A quick google search tells me you can get stun guns for a whole hell of a lot cheaper, but if you're more likely to have this in your hand and ready to use when needed, can you put a price on that?
B) 650,000 volts seems like a lot, but in comparison, maybe not. Some of the mid-range stun guns can put out over 10 million volts on a full charge. But still, 650,000 volts is better than none?
C) It has a safety switch. Good call.
What do you say? Is this something you'd invest in?