I have done 3 features with multiple REDs on set. I simply send guide track to all the cameras via wireless. The camera audio is used to sync the multiple cameras. One camera audio is then used to sync the multiple tracks of audio from the recorder (manual mode) or just use pluraleyes to auto sync everything. Never had any picture or audio sync issues. Never used or needed to use TC or a TC slate because the guide track is more accurate than timecode since both are sampling at 48,000 times per sec and there internal clocks are very accurate. I have done 2 hour events (continuous record on cameras and recorder) without any issues. TC was invented for a system that uses a time base corrector that generates a master TC which then sends that TC to the camera (gen lock) to permit switching cameras (it is no longer required in switches because of other techniques). The cameras then sync to the master and all cameras snap a frame at exactly the same time so switching doesn't occur in the middle of a frame. WIthout gen lock TC running from the internal clock on each camera will be off by design.