Apparently the build quality of the Schubert is not that great when seen close up. The door is hinged at the bottom, like the Polish Smyck (?) so it is not that easy to get in or out.
I know almost no German, but that sheet seems to say that it was built by Schubert in Hainichen or Munich(?) DDR in 1958, originally with an IFA or Ilo 350 2 cylinder 2 stroke air cooled engine, then with a Heinkel 175.
I don't know if Schubert was an individual, team, or company effort, hope someone knows a bit more about it!