Each of the Faber houses distinguished their products in some way, and from what I’ve seen, the holders for Johann Faber’s waistcoat/pocket pencils were often ornamented with metal figures. In this case (or perhaps, on this case) it is the Eiffel Tower:
There are two writing instruments inside: a pencil and a dip pen. But rather than being housed in the ends then flipped around and inserted into the holder to extend them, the two items are connected in the center; the cap then becomes the extender:
I don’t know whether this item was made specifically for Johann Faber’s Paris store, or whether imagery of the Eiffel Tower was appealing to customers in general, or perhaps both.
The other end holds a flat cedar pencil—whose width and height are resistant to other manufacturers’ refills, even (or perhaps especially) if they were made by your brothers:
Everything about this pen/pencil is very finely made, but trying to hold and write with it as a pen feels awkward. My fingers naturally want to grip the flat sides of the holder but due to the orientation of the nib, you have to hold it with the flat side facing upward — the nib can’t be rotated in the holder.