My self defense knife is a Smith and Wesson shield. No interest in bringing a knife to a gunfight. And if youre justified to use a knife on somebody, youre justified to use a gun.
There are situations that require a knife to get to your gun. One such situation is someone notices that your carrying and attempts to snatch your weapon. In weapons retention training, you will be taught push the butt of your weapon down locking it into the holster, draw your knife from the off side an use it to get an attacker off you so that you can draw your pistol. It's just one more situation that if your prepared you can survive.