I've seen that before. I believe that the little Adler was used for a paymaster or for non-military administrative personnel. I'm not sure that I would trust the helmet though. The stitching doesn't look right and the seller has done just about everything possible to keep from showing the top of the helmet.
Prussian Beamte officer helme. We have discussed these military administrator helmets before on the forum. Many states had them, all with the basic Dragoner helme characteristics and all with some sort of contrasting miniature shield or Prussian eagle on the main wappen.