Roland, you asked for info on Otwin guitars; this is what I found on the web; Otwin was an instrument brand name used by the Otto Windisch company in Germany after world war ii and lasting well into the 1960s.

The Otto Windisch company was founded in 1886 with Otto Widisch himself as the sole owner until 1903 when his brother, Paul Windisch, joined the company as a co-owner. Otto Windisch died in 1935.
By the mid 1920s the two brothers were still running the company, manufacturing violins under the OW trade mark and other stringed instruments under the Owi, Edelklang and Joachim Tielke brand names.
Windisch was one of the few German music houses that managed to survive ww ii.
Guitars branded Otwin included arch tops. Although the cheaper ranges seem to have been just cheap plywood guitars, there are examples of the high end models being very nice instruments made from good materials.