Photos, please! How "identical" are the Remo and Merkel drillings? They may be only of the same Standard Suhl design. At least, the gun with the inscrition "prime steel" in English was certainly originally made for export. Most Suhl gunmakers got their rough forgings from the same sources, either the Sauer or Schilling forge. Many farmed out work to the same independent action filers, stockers and engravers.
I have asked around German shotgun collectors. Noone in Germany has ever seen a GEHA-type shotgun with the "Hard Hit Heart" logo, so IMHO this was the mark of an American importer. Alas, appliing funny names to guns was more an American custom than a German. Remember the also 1920s Mossberg "Little Brownie" pistol, named for a then-popular cartoon?
BTW, ecept for those shotguns, the GEHA logo is unknown. But the magazine conversion is different from the REMO guns. There were two German patents for such conversions, one issued to Gebr. Rempt, the other to Emil Hengelhaupt. As the GEHA guns are made to Hengelhaupt's patent/design, Geha may stand for "Gebrüder Hengelhaupt". No less than 44 Hengelhaupts are listed in the Suhl/Zella-Mehlis guntrade. "Ge Ha" is what a German speaks when he reads the letters G and H.
