After spending quite a bit of time setting up a QD from Trier towards Wittlach, I have decided that they are not worth the effort for the following reasons:

• Buggy operation of AI markers - don't work in 64 bit mode editor sometimes.
• No fine control of AI consists.

In a standard scenario, you have control of every aspect of the scenario, including timetabling, train priority, train functions through LUA scripting, etc.