Full disclosure: I don't have a drop of blood from any Balkan country in what was the former Yugoslavia, and no dog in that fight.
I shoot and reload PPU cases in multiple calibers and own and collect Yugoslav arms from various periods. I've also shot and reloaded Igman ('IK') ammo and cases.

PPU has been at it since 'Yugoslavia' was the Kingdom of the Serbs, Croats and Slovenes. It had it's beginnings in what could be considered the Golden Age of 'Yugoslavian' arms and ammunition production and innovation. There was a lot going on there at the time that is more specific to Mauser rifles, 7.92X57mm ammunition and the conversion of foreign weapons to an 8mm standard, but that's obviously beyond the scope of 5.56 ammo. Look up Jakob Poshinger, FOMU and PPU's beginnings here for a brief look. Want more? Get ahold of me and I'll oblige you:
https://www.prvipartizan.com/history.php

No offense, but I think you're short changing them. I've found PPU ammo and cases easier and better to work with than Igman products. I've encountered flash holes in Igman cases that are Euro spec, and of the type that will snap or bend your decapping pin. I've not had this problem in PPU cases.

Since the breakup of the former Yugoslavian states, PPU went more commercial and has a wider range of ammo and components available. They outproduce Igman and have a significantly larger market presence, in both the loaded ammunition space and for reloading components.