No. A ballistic knife is just plain dumb.
But a Vietnam Tactical Tomahawk that you throw at people for an instant-kill, regardless of where you hit them, isn't...
I'd like to suggest a high-powered revolver kind of weapon for the fourth handgun. It is exceedingly powerful for a handgun, but features a Fixed cylinder design with a capacity of five. It would either be based off of the Biggest, Finest Revolver, or the Pfeifer Zeliska. Or, maybe you could go for the Thunder .50 BMG pistol, with a loading gate on the back with a capacity for one bigass cartridge. These aren't production firearms, however, so I sort of doubt they will be added.