Erfurt with British proofs

[Dave Sanders]

Just picked this up today, couldn't resist, but I can't find much information on these lugers other than when these were sold into the public, the proofs went on. What is the story about these. This is all matching except mag, and the grios are marked 72 instead of 82. Also, what is the stuff that looks like a coating over the blue? Do these hold any value other than a shooter status?
Dave