An Amphicar buddy of mine from the German Club has a couple of the originals. They are indeed awesome. Did you know the first prototypes, cobbled together by a fellow named Fritz Fend, started off just after the War, when Germany was still banned by the Allies from making powered vehicles, as pedal-driven all-weather rides for the disabled? I believe they were canvas-covered. Later Fend hooked up with what was left of the Messerschmitt aircraft concern, got permission to use engines, and they took off from there. They used to race these things fairly competitively in rallies and so forth. I seem to recall a four-wheel model called the Tiger (?), which could handily outrun the hot Opels of the day.
If anyone's super interested in the breed and reads German, I believe I could dig out a nice article on them from the '80s magazine, "Markt für klassische Automobile und Motorräder" that I've still got somewhere, since it also has a feature on my Zündapp Bella scooter.