Wow, what an amazing spot! As far as I know, only three of them were built and one of them was soon destroyed. It was long assumed that a second vehicle was also destroyed shortly after the war and that only one of the three vehicles still existed. However, enough parts of a second vehicle were apparently found to rebuild it and this is probably the vehicle that can be seen here. As far as I know, it's actually in the Porsche Museum in Germany, I'm a bit surprised to see the car now with a Baden licence plate (and a plate that was previously on another Porsche).
Thanks! I knew the car had to be somewhat rare, but I was expecting it to be a low-volume production, not a "prototype"! The article was also really interesting, thanks for the info!