Hornady CD is not, in and of itself, a gimmick. It is an inferior self defense ammo though. The company even states themselves it was not designed for ANY barrier penetration. It is designed for quick and reliable expansion. Whether or not it does this under conditions when we need it is anybodies guess.
LE agencies dont use it because of the barrier penetration thing. It also will not penetrate 12" of gelatin. Once again, Hornady is not saying it will. If you read between the lines you can tell it is an inferior round marketed towards defensive carry and nothing else. Hornady has their TAP line to market to LE.
In the end my conclusions are to use something else besides CD. Even though everyone likes to condemn it, the Federal Hydra-Shok is a superior round than CD. LHPs for 38 special are a round no one has been able to really find a whole lot things against yet people dont used it for reasons that are beyond me. I use it and the great number of tests I have seen involving it give me great confidence in it.
Federal HSTs are also a superior round to CD. They will penetrate the 12" even if they dont expand. This is better than the CD which probably also wont expand but wont penetrate as deeply. CDs are loaded a little light I think to help out Joe Average CCW.