Solid dlc, does not add too much, but also not that expensive.

Assuming you already like Hearts of Iron IV, I strongly recommend this DLC. The four nations expanded on here (Hungary, Czechoslovakia, Yugoslavia, and Romania) are in risky positions, but are therefore extremely rewarding to play. They provide real challenge in a way that the game's major powers don't. It is exhilarating to be engaged in an uphill battle for survival, both politically and militarily, and when at last costly victory has been achieved, it will feel truly earned.

When you produce equipment and then you research new equipment, it used to be that you'd send the old equipment to your puppet, to reduce their autonomy. With this DLC you can convert that equipment into the newly researched one, which saves resources. Vital If you're playing with the Axis. The new focus trees for the Balkans nations is quite nice and historical with options to go alt-historical. I wish Bulgaria was included here, but they only have the generic tree.