Not my favorite overall knife, but
this blade shape is perfect, I think.
Why?
The reason that I ask is that context is everything here, as many things can be used to kill a person if the desire is there. Besides the ability to kill (which is pretty much a given), the needs of a certain culture dictate what is desirable and what is not.
This makes a lot of sense in a prison, but not so much to me after work. It's constructed of a readily-available material that cannot be detected by wanding, is easy to work on a concrete floor, and there are ways to conceal such a thing that make detection by a pat search impossible and increase its lethality at the same time. I won't go into those here. It will do a fine job of killing someone, particularly when they're not aware that an attack is imminent. If the attacker is HIV-positive and thoughtful enough to smear some blood or some such on it prior to using it, the killing blow need not even be serious in nature to be mortal.
(This is pretty tame as far as shanks go, by the way. I've seen ones that are far better.)
This doesn't appear to be much unless you're fighting someone in harness; then, suddenly, it makes perfect sense. What better to lever and pry your way through plates of steel than with what's effectively a steel rod with a point on it? You're not going to chop through all that crap, you'll need to find a way around and through it and a rigid, pointy weapon that can accomodate a second hand partway down the blade to improve control and leverage is just the number for that. Again, it's not much use to me, but to someone else five centuries ago...
This is clearly inappropriate for concealing on my person on a trip to the grocery store, but that's not what it was designed for. The individuals that these were issued to had other concerns. It may not make as much sense now but it made perfect sense at the time.
When we compare the various attributes of weapons throughout the ages, it's important to remember what any particular group of people needed at that time, and why, making a description of the logic involved somewhat important.
But that's the beauty of open-ended questions, isn't it? There's always another answer, and sometimes that answer is just another question.