I believe I've seen one or it may have been another ASR razor very similar to that. It was part of a collection of 1,000 razors. I spent 5 hrs at the guys house trying not to drool. He had been collecting for over 20 years and said to the best of his knowledge it was one of very few prototypes. I obviously can't verify the accuracy of it being a prototype but I'm fairly certain that it is at least quite rare.
Here is another rare razor from his collection.
Another pic of that razor.
Here is another rare razor from his collection.
Another pic of that razor.