I don't quite see the point of being able to define milestones in the overview that are not in any way related or dependent upon the "real" milestones or tasks within the task section. If part of the project is delayed I have to remember to update the overview milestones as well. It would be better if the overview would show the "real" milestones from the task section. As an alternative, it may make sense to be able to checkmark a milestone if it should be shown on the overview or not (Default = true) in order not to clutter up the overview too much with "not so important" milestones.
Thanks for your feedback.
What you see on the Project Overview are Decision Points rather than Milestones. Decision Points are typically fixed in timelike go/no go decision and outside the time plan of the work performed in the project itself.
It's a nice idea to be able to show some of the milestones of the project on the overview as well though.