With a sterling silver grip section and blind cap the M625 Red is a different beast to the rest of my M600 pens. When I first bought it it took me a while to get used to its added weight and metal section. The red body is too dark in my opinion - I have to hold it in front of a bright light to see the colour.
Another old M600 extra fine nib, this time a 18K version from the M620 series of pens - Its not quite as problematic as the previous nib but it still produces a very fine line.
Last time I had this ink in rotation it was in a Sailor 1911 Medium with a H-F nib that writes with a hair width line. This time it is not much better to show off the properties of this ink. Maybe in 2½ years it will get used in a broad nib. An interesting olive green tone but no hint of shading or sheen from this nib.