^ IMO, the reviewer failed to talk about the most important question. He mentions that the 701d will sync with a GH4 via hdmi, but he doesn't say if it holds sync for an hour, two hours, or the entire time they are connected.
About 13 minutes into the video review, he said he jam synched the 701d with a Zoom F8, disconnected them, and checked the sync after an hour. He appears to say the Tascam drifted 5 seconds ahead of the F8. If they had stayed connected via the BNC input, would they have stayed in sync? If a pro user has an external timecode generator, they would want the 701d to lock and stay in sync with it over whatever time they are shooting.
I'm hoping that the 5 seconds of drift he mentioned is some sort of testing error. When I compared drift betwen my other Tascam recorders vs. my video cameras, I found drift of a few milliseconds over an hour, not 5 seconds.
Since the key feature for the 701d is syncing audio to video, it seems to me that the key question is how well the 701d holds sync to video. Best I can tell, the question of drift isn't 100% answered in the review.