I've not flown a DA-42, but in terms of multi-engine training, I hope that's not the first time students are seeing a prop lever. If the student's are doing add-ons, then they have to have complex time (where an adjustable prop is required). If however, they are doing everything in a multi, then that is a major blow to their experience. Make sure they have a really good grasp of how changes in prop pitch are controlled and why they are beneficial. You could even go so far as to teach the same way you would for the baron and then, once they understand the principle, explain how the DA-42's FADEC operates.