This is a very rare accordion, which you will see very infrequently, if at all. It is a well made instrument with the inlay both extremely well-done and quite handsome. Both the healthy bellows and the sound make for a very pleasing playing experience at any volume.
I have been unable to find literature on this accordion, and would be delighted to do so. It was made in Germany by Herrmann Buttstädt, but the precise year of its manufacture cannot be said with certainty, although its style is typical of the 1920s, which corresponds with the accepted period of the maker's work.