In terms of diving skills, the DMT and IDC do very little in terms of making your dive skill better. These are not about you, but at making you a dive professional to help others with their diving. Many instructors that I know state that teaching has actually ruined their skills since doing the skills (per some agencies) has very little with true diving.
Sure, repetition of many of the skills might help you, but then again, these skills should already be at a level that you don't need help.
Now, with that said, I tihnk that being a DM or Instructor and being around students/new divers can really help your situational awareness. When I was a DM, I had many "ah-ha" moments. These are the moment when thinking back to rescue class the book describes the situation one way, but there is not good way to simulate it. Once with students, you see all of these situations develope exactly like the book says they will. Armed with this knowledge, you can start to head a lot of stuff off before it developes into something worse.
In terms of the length of the DMT, try to find out if you will be doing training with real students or simulated sessions? With live students, you are sometimes at the mercy of when the classes are scheduled. At the shop I work with, we only have open water dives for 6 months of the year, if the DMT starts during the off season, the person will have to wait for the classes to finish up. Also, depending on the volume of DMT going through the course might impact it as well. If candidates are observing actual classes, then too many candidate actually becomes a problem. I wouldn't judge the course based solely on the length of it, but instead, ask some questions.