I've used Hydra-Shoks extensively for years. I've shot through windshields, car doors, construction materials, into kevlar, etc. For a non-bonded bullet, they're pretty decent. Hydra-Shoks do have issues with the tip clogging in clothing, and they do have really definite jacket separation issues, which leads to fragmentation problems. They are decent enough for going through intermediate hard barriers like winshields and such, but there's noticeable spalling and deformation, which makes the following penetration into your perp shallower.
With that being said, I still wouldn't want to be shot by one. In most circumstances, the Hydra-Shoks perform quite well for what they are and for being essentially antiquated technology. Basically, as long as the bullet is capable of penetrating at least 12" into ballistic gelatin, it's sufficient. The Hydra-Shok does, so it works okay for personal defense applications. For 9mm, the advantage comes with penetration, so as long as your round is still supersonic and you're not using target FMJ ammo, you're generally fine.