Bartek, It's a scratch track - there is some bleed, but you can make it work ok and reduce it to minimum with careful gain staging. don't know about they A7s II or ninja flame, but with a Blackmagic Pocket Cam you can adjust input levels independently, which helps. Works ok for onset playback, but wouldn't want to use for dailies and certainly not for editing.
The Tentacle Sync Software works great with that kind of setup as it automatically senses the Audio TC Track. It's super easy to use with multicam projects btw.
+1