I looked at these ballistic knives when they first came out about 20 years ago or so and I thought "what a POS". I have faced people armed with a number of different weapons over the years, and this rates pretty far down on the list of things I'm worried about.
GREENJACKET, you are correct, it does not work well and best of all, the person disarms themself when they "shoot" the blade. (I think it was originally marketed as a KGB or Russian special forces knife).
I think what prompted all the legislation in the US was the knife was portrayed as such a deadly weapon on a couple of television shows that our legislators, in a typical "knee jerk" reaction, passed laws against owning one.
mike