As I see it, courses with flags/markers are pretty often not as good as the ones without. Those are usually planned in larger use base in mind (juniors and old farts) and often not that hardcore technically. When there is snow there will be tracks leading straight to control, that's annoying when you try to navigate yourself. And so on.
The biggest problem with no markers trainings is you easily end up planing courses by yourself, so you know in advance what kind of legs there is and what are the route choice options. To get around this issue I did set up here on AP a group called course exchange for meeting place for runners to plan courses for each other. It just did not fly very long http://www.attackpoint.org/group.jsp/group_166
Maybe time to wake the group up again.
It is pretty essential to get used to do runs without markers. And it is good for ones technique, you will not find controls by hitting it by luck - even if you hit the right spot by luck you often just run by because you don't know you were at control.
My favorite middle distance technique training is actually control putting chase interval training, with pairs. About 1 km intervals with 3-5 controls. you start first with markers, your pair starts 60..90 secs later and picks markers up and tries to catch you. The start gap is supposed to be big enough to easily stay ahead if you don't hesitate or make mistakes, and you even have couple of tens of seconds to use for making sure you place marker correctly or play safe once. The key here is the pressure you get and feel for knowing you are being chased and there is no room for hesitation or mistakes, but you still are navigating on your own (not running head-to-head with visual contact). At last control you wait and see how many seconds later the chaser arrives, so did he come closer or not. He hands over markers he picked up and you continue with next set of controls. At halfway we usually swap turns, chaser's turn to go first and put markers. One good thing here is you are not supposed to have markers out there and you can have map exchange and plan the intervals you will chase, so the course is all new the the runner who goes first and puts controls.