We know that the types of protection we have witnessed worn all have serious shortcomings.
Personal forcefields simply don't appear to be technologically feasible. TAS has the belt-projected "life support fields", but those are incapable of stopping a phaser at stun ("Slaver Weapon"), and offer little protection even at fisticuffs ("Pirates of Orion"). TNG shows Worf rigging a comparable field that can barely stop a few low-speed bullets before frizzing out. And when the Borg Drones appear, their phaser-proof fields impress the heck out of our heroes.
Body armor as worn by Klingons has been shown to be vulnerable to disruptors and phasers (a single shot always takes out the warrior), but also to knives and swords (again, a single stab easily penetrates, with fatal results). The same is true of TNG spacesuits (ST:FC), and supposedly of their predecessors as well. It doesn't seem as if these things could stop bullets, either - simulated Klingons fell to simulated WWII bullets in VOY "Killing Game".
Now, it does seem as if 23rd or 24th century technology ought
to be able to come up with armor or forcefields that can stop a dagger or a sword. I mean, even medieval chainmail achieved that much on occasion! Stopping of bullets might be physically impossible with mere armor, though (or we'd have done it today already), and perhaps not worth doing with forcefields (because the enemy would just whip out the disruptors if the slugthrowers failed).
But what is
that Klingon armor good for? It doesn't stop beam weapons, it doesn't stop edged weapons, it doesn't stop bullets. Heck, there are episodes of DS9 where a fist driven in an armored stomach makes a Klingon fold in two! Are those thickly padded vests intended to be flotation devices? And if so, what about the comparable TMP Starfleet "armor"?