TLDR: It’s awesome and you should probably get one, too!
When I first started seeing these I thought they were pretty silly, but after hearing an explanation for their use my opinion of them slowly changed. If you haven’t heard Kabar’s sales pitch, the purpose is to violently distract someone who’s going after your gun.
For example, let’s say you were to be physically accosted by someone, and, upon reaching to draw your gun, they start trying to disarm you. The TDI’s purpose is to be carried on the weak side and drawn with your weak hand, and used to deter the person by slashing at their face. So your strong hand would be gripping your pistol, and the assailant would have both of his hands on top of yours, trying to prevent you from drawing. And with your weak hand, you would draw the TDI.
While this sounds like overkill on the surface, it’s actually the likeliest scenario that we as daily carriers would face. If you’re at all familiar with the laws, you know it’s virtually illegal to draw on an unarmed person until you actually start taking damage, at the earliest. By which time, the chances of being disarmed and shot with your own weapon are extremely high.
As far as effectiveness, I think it’s probably highly effective for the role it’s intended. I don’t know if anyone’s ever used one in real life yet, but having someone slashing at my face with one would, I believe, cause me to involuntarily use both my hands to defend against it. Sharp metal objects in people’s eyes tend to have that effect on them, so probably doesn’t take a genius to rightfully conclude it would work as advertised.
Use case aside, the knife is extremely comfortable to carry in its intended IWB appendix position. I opted for the smallest one (called the Investigator), and I forget it’s there. It conceals very well under a T shirt, and it doesn’t dig into me even when sitting or bending over.
It’s also very fast and easy to draw with your weak hand. The shape and position and mode of carry are all very conducive to making it easy and intuitive.
My one complaint is the factory sheath. It’s downright useless, and you should plan on getting an aftermarket one. There are many available, and they all look pretty capable. I got mine from T5 Custom, and I think it’s extremely good for the price, and just in general. They also delivered in the timeframe promised. 10/10 would recommend them.
P.S. If any of you artisanal types out there are reading this, I would LOVE to see G10 grips available for these knives. The factory plastic grips are adequate, but they lack any useful texture, which seems to me to be an oversight, considering the use case for the knife must presuppose that any actual use would by default mean the entire knife, handle and all, would be covered in blood. I’m sure Kabar resisted the urge to use G10 out of cost concerns, but I think most people would see the benefit of them.