Alfred Arnold was the only manufacturer of this type of bandoneon.
The shown instrument appears to be in a very good conservation state.
It is not common to see engraved button key codes on a unisonor
bandoneon, since they were created for the
bisonor bandoneon. Probably this happened while the instrument was
refurbished. The finish looks handmade.
but take care: you can't convert both models simly, because the reedboard need the corresponding chambers.