Two ways to look at this Crab. The two things you mention have already been highlighted by myself. Autos can be exciting with NR control and sloping ground with an aircraft that has no MRH is easy to mess up. What it means is that the students will have to get good at it before solo. It may take a while longer than before, but so will twin engine factors as well. As for running them all day..... why? It's so quick and easy to start, you don't have to run it all day