How good are MiMs in Germany in terms of increasing your employability and career opportunities? Are they valuable there, or would I be better off with a different type of degree? I'm looking to switch from engineering to management, hence my interest in this.

If you speak the language and your goals are relevant to the degree, then yes, but if you're just looking for a degree that will increase your employability and there's no other reason, then it might not be the best approach.