The AFF Universe Wiki also has an article on this topic: UDP Infantry Weapon

The ULA exclusive pistol.

The UDP may not deal much damage per shot, but it's quicker at firing said shots than it's rival pistols (the Avex EVP and Sikfrit Model 54).

And with it's exceptionally fast equip time of 0.35s, it's more than handy if your mag runs dry or you overheat your main weapon in the middle of combat.