Yes, I did the course some years ago when it was held at Elveden.
As its name implies, it is a Deer Management course and not a Deer Stalking course, so I found it very useful from the perspective of understanding different aspects of managing deer - interaction with landowners and the public, population studies, forestry and other land use, etc. From that perspective (compared perhaps to the DSC1 and 2) your knowledge of stalking deer is of marginal advantage. What this implies is that the course requires a significant amount of pre-work and study on the course itself.
The attendees came from a wide variety of backgrounds, including DDM, farmers/landowners, deer farmers, forestry professionals and a smattering of deer stalkers. They were there because they wanted to take the course, not because they needed it to get their FAC (e.g. DSC1) or stalk on FC ground (e.g. DSC2). That meant it was a very interactive course with a lot of discussion and differing points of view, something I found really interesting.
There was/is an advanced shooting test, but it was optional.
I didn't take the course to give me any sort of advantage when it comes to finding stalking, but I have subsequently used numerous aspects of the course that otherwise would have been a real challenge (deer population modelling, etc).
Overall I really enjoyed it, but then I am as interested in all aspects of deer as I am in deer stalking itself.