Having seen some videos of this...the channel is sloping so the honey runs to the back of the hive for extraction via a tube which you insert...first removing a plastic bung....for which pliers may be needed. The bung leaves a small opening and any remaining honey can run out of the channel and into the hive.....the bees can lick the honey up as it leaves the channel. Failure to fit the tube into the channel correctly ....for instance fitting the wrong end of the tube into the channel, may leave this opening unprotected and your honey will run into the hive. I believe this is shown when a numpty connected it up wrongly.
I have recently seen video and pictures of some of the new Flowhive frames in use...full of capped honey. The bees will fill them the same way they fill any plastic frame. I used plastic frames for the first time last year. I painted them with some of my own bees wax. The bees built on them immediately and used them for stores too.
I would think that some of the people using the flow frames have been rather impatient and used them on small colonies and / or when there isn't a flow of nectar....but then you wouldn't expect honey in those circumstances whatever type of frame was used.