The mic synchro start works surprisingly well! When the recorder sync- starts, it does also record a short moment of the signal that preceded the point of activation so the beginning is not clipped. (like a mini time-machine feature)
If it does sync-start at all depends on the current gain settings, so it might be neccessary to adjust gain a little bit up to be on the safe side.
It stops recording after about 3 seconds of silence which are not cut away, the 3 seconds are left at the end of the track.