I see a number of good things in this DLC, but also see a number of problems.
First thing I spotted was the V3/V4 in the light tank tree. Hungary purchased (I believe) 2 such vehicles from an Austrian company for testing purposes, and rejected them. They went with a Swedish design instead, which became the Toldi (the Toldi II was essentially the same tank, only made completely in Hungary, while the Toldi III was up-gunned from a 20mm AT rifle to a 40mm cannon). Putting the V3/V4 in the production list as a required step before building the Toldi makes about as much sense as requiring the US to build "Locomobiles" (which were harshly rejected and their insistent producer heavily ridiculed by the US Army) before instituting the "Jeep" as the standard light vehicle). BTW - one earlier poster questioned the "hat" on top of the Toldi, which is actually a radio antenna loop. Hungary had begun deploying radio equipment throughout its armed forces in 1934, contrary to HOI not crediting them with it.
Incidentally, while somewhat similar, the armor tree in the Hungarian mod seems to have several details right which the official Paradox tree appears to have gotten wrong.
Reinstating a Habsburg monarch was briefly considered in the early or mid '30s, but the strong political backlash against the idea from several neighboring states led to the conclusion that it would trigger an immediate declaration of war by the Little Entente and France, who were adamantly opposed to any such return. Making it a possibility in the NF tree should bring SEVERE relations issues and a strong possibility of an immediate war. Admiral Horthy (Regent after the removal of the Bela Kun Communist government) and several cabinet members basically vetoed the idea at that point. There has been some speculation that while Horthy himself was not eligible to become King, that his eldest son might eventually have been elevated to inherit the title, had he not been killed in a plane crash later in the war which many speculate was caused by Germany.
One cannot equate "Fascist" with "Nazi" in Hungary, as there was a definitely cold relationship between Hitler and Horthy, and a sense of needing to appease Hitler just enough to stave off an invasion of the country by implementing "halfway measures" on Hitler's demands. Many refugees fled from Hitler's early conquests to Hungary (who admitted them despite Hitler's demands to the contrary), some taking up residence in the Budapest area. Hitler's stubborn defence of Budapest near the end of the war may have had more to do with needing more time to "collect" those people than in any sense of strategic necessity or support for an ally. While Horthy may have been a "right wing" authoritarian, he was also enough of a humanitarian to have defended Hungary's Jewish population to the best of his ability without provoking an invasion, and eventually Hitler tired of the "game" and invaded anyway.
The Communists still had some backing, despite the string of brutal murders conducted by Bela Kun's Communist party in its grab for power, but any strong support had for the most part been crushed by the equally bloody retaliation by the right and center factions. There probably weren't that many people willing to go through that again.
The Little Entente (CZE, ROM, YUG, with French backing) was designed specifically to prevent the reinstatement of the Habsburg monarchy and the return of either Austria or Hungary to prominence. Both Austria and Hungary were intentionally landlocked after WWI, even if it meant turning the coasts over to Italy, which had virtually no ethnic representation in those areas. The Little Entente began to fall apart after around 1933-35, but was still in existence on paper, and would probably have become relevant and active again if conditions had warranted it: the return of the Habsburgs or any territorial grabs by Hungary. All 3 members clearly felt threatened by Hungary's repeated (and consistently ignored) requests to the League of Nations for plebiscites (hinted at in the League charter) in its former territory to allow the residents to freely decide to either remain parts of CZE, YUG, and ROM, or return to Hungarian control, and CZE tried to force a resolution through the League to punish or disband Hungary over it several years before the start of the game. There was also apparently some communication in the mid '30s with Slovenian separatists about breaking away from Yugoslavia and becoming a semi-autonomous protectorate under Hungary, giving Hungary access to a port without actually owning it, but I see little chance that any of the three neighbors would have surrendered territory voluntarily without a fight or outside pressure (as eventually happened in CZE).
There seems to be a shortage of material in English, but former US Ambassador to Hungary J. F. Montgomery's book "Hungary, the Unwilling Satellite" seems to provide a more neutral (but sympathetic) outside view of the events leading up to WWII from a Hungarian vantage point.