This is a very interesting thread. I didn't realize there were so many of these German bikes around. Back in the 80s when I still lived in Slovakia, my friend was working for the Koliba TV studio in Bratislava. He once showed me around the props warehouse and I saw a couple of R75s. That was the only time I saw them. Riding one of these back then would've been considered bad taste since they were used by the occupying forces during WWII. Soldiers riding in those were like sitting ducks and usually the first to be killed. The resistance fighters (partisans) would sometimes set up a steel wire across the road, high enough to decapitate the rider and when the bike went off the road, they would attack the rest of the crew.
This is a true story that happened in my grandfather's hometown towards the end of WWII. A young German officer and his private were riding one of these bikes and were attacked and killed by the local partisans. The officer was the son of a high rank general and the father showed up with a whole army unit and lined up all men and boys older than 10. My grandfather and two uncles were in the line. He was threatening to shoot every 10th person from the line unless somebody gave him information leading to capturing the partisans. Luckily the local doctor happened to be German and he managed to talk the general out of going ahead with that. After the war when communists took over and started doing purges and fabricated trials just like Stalin did, the doctor was accused of being a collaborator. So the poor guy was sentenced to hard labor and ended up spending many years working in uranium mines. That's what he got for saving 20+ lives.