I just went hiking with Hiking Istanbul- a Facebook group. and thought I;d warn you about the following:
- they customarily trespass on government property- which got us in trouble with security forces today, and could potentially get you arrested;
- they hike off trail and on wasteland;
- you're on your own when hiking, with little help from group leaders;
- they may make you do things like cross highways.
Very little concern for safety overall. I have been hiking for a long time, and have never had such an unpleasant experience. In my humble opinion, they are complete amateurs, I would avoid at all costs.