I'm not an expert on Romanian organ building, but I would guess that these instruments don't have any independent stops on the very short pedal compass, and the pedals simply pull down the corresponding keys on the single manual.
Therefore, the only "mainstream" organ repertoire you can play on them is music for a single manual only, with the advantage of being able to hold sustained notes in the bass, i.e. "pedal notes" ... [face-palm].
Small Italian organs were built in this style in the 17th and 18th centuries. Here's a page from a collection of pieces by Domenico Zipoli, for example. Fun fact: Zipoli, 1688-1726, was Italian by birth, but spent most of his working musical life in what was in his lifetime part of Peru in the Spanish empire, but is now part of Argentina!
Historically, organ building styles have always been different in different countries. There were no instruments of this type in Germany or France, so you won't find any French of German music written for them.
Another possibility for a different style of music would be to ignore the pedals, and look at some late-19th-century music written for harmonium. There are original compositions (not arrangements) for harmonium by organist-composers like Franck, Guilmant, Karg-Elert, etc, and later by Hindemith - and even a few pieces by Liszt and Elgar!