The horror? It works ok, but here are my bugs.
1. Must be close for it to chase you. Doesn't chase you from far away.
2. Sometimes freezes in place, moves again if shot.
3. Doesn't harm other npcs? Combines/Rebels are never killed or hurt by it.
Those are my bugs, but nothing that worries me really.
Oh yeah, the bloodsucker has the animations of the fast infected too. Don't know if you noticed that or not.