When Merkur started offering adjustable razors, they offered them in a variety of versions.
The model number of this particular version was a 520. There was also a 580 which was the same razor with a leather case. (See HERE) This particular one seems to be a mixture of silver and gold plated parts. The topcap, adjuster plate and dial are chrome plated, and the rest of the metal parts are/were gold plated.
Its a typical Merkur Progress design with the lather channel except that it was made out of a (brittle) plastic called Pollopas. Fortunately this one is free of any cracks.

This is one of the very first Progresses and was made in either 1955 or 1956.
Looking at the baseplate, there are a few differences between it and the other versions.
Firstly, the logo looks like it has been engraved i.e. debossed as opposed to embossed and is on a bit of a raised section.
Secondly, there are two small square cutouts where the two side tabs of the middle plate push down and the one cuts into the word "GERMANY".
This doesn't exist in any of my other Progresses and leads me to believe that it was manufactured before their moulds were made/ready and that the base came from another razor within their line-up at the time. I thus believe this to be one of the first Progresses or at least very early version.
Further digging around online brought me to the "601" (Last image on the second row below). I believe that the base came from this razor.

How does it shave?
It's the same as the normal Merkur Progress but it has a slightly different balance. While actually shaving I could not tell the difference.

The Unboxing!
The below images are what I took of the unboxing. The Merkur blades are correct for the period but they only gave three blades of different thicknesses. The first owner must have decided that he liked the 0.06 blade and bought a tuck of them.
The Mulcuto blades may have been correct for the "era" but they would not have been included in the package.