I have some problems too with my phone and the FC40 app... it connects fine but after closing the app my phone WiFi settings go crazy, half of the time I have to manually connect to my router again because it refuses to auto connect to anything beyond the FC40 camera, I think the problem it's that the app is a little bit old (2013 I believe).
This is my first drone that I will say fit's on the "this is not a toy" classification and I'm not ready to put a GoPro on the machine and see it crash against a tree (I keep practicing with my SymaX5C the crashing technique!!!)... so the little DJI camera should be enough for the moment, I installed the Walkera gimbal and I'm working on the design of a small bracket to hold the camera, 7.4V LiPo pack and step up regulator in place of the GoPro.