It's not to say that Mechanical Engineering solely is not up to par and Mechanical Engineering with Management is the shizz
However, the latter has obviously extra credits. The world is moving towards having a good grasp over interlinked fields of study, like a Bachelors in Biological Science is more valuable with a Bachelors in Microbiology in terms of employment opportunities and further study. Not because a Microbiology student knows any less about Microbiology than a Pure Biology student; in fact, you'd argue, he knows in way more depth.
However, in practice, a Microbiologist will not solely be dealing with a virus in a petri dish all day long, independent of external factors. To study its effect on lifeforms, he may need in-depth information about the metabolic processes in animals and plants, and the implications different species of animals or different classes of plants have that have to be considered. He may need to understand the dangers of adding or replacing bacteria in the environment, or the chances of mutations leading to genetically-modified bacteria.
All of these are not solely Microbiology; and so a Biologist would be all-round suitable for just any kind of profession, because he knows of everything sufficiently.
Same goes for Mechanical Engineering with Management. An engineer will not always have an ample supply of money which will never extinguish; he will want to work his plans and projects in a way that they are most economy. Money management is very important, hence a student having extra credit because of that will seem more prolific for an industry than otherwise.
However, it does not mean Mechanical Engineering is useful, just as Microbiology Majors are still studied and quite useful. If you have an offer from Edinburgh, for this subject, take it if you can. And best wishes!