i think this is going to be dependent on your first comment, of "how are you going to use it". the tactics used will be the determining factor on the the usefulness of the weapon. i think a jacket will limit the effectiveness of thrusts like you say, but will actually limit slash cuts more so. its very difficult to say whether thrusts or slash are more effective because the goal is to stop the threat. will a slash have the emotional demoralizing effect needed?? maybe. but the chances of hitting something that will make the assailant bleed out quick enough is pretty slim if he is determined to kill you. to be honest if your using a knife in a violent encounter where lethal force is required your pretty much screwed.