I think that it would be pretty useless. Not enough velocity to be much advantage and the bullets they use have done a heck of a good job for the past 150 years.
On the filp side I am really surprised that all the big manufacturers don't make such a thing anyway. They could charge a fortune and everyone would at least have to try a box or 2. Some people would swear by them no matter the cost or actual preformance just for the Mall Ninja factor.