Had a TV remote app on my Note 4
said app could be activated from the lock screen without entering PIN - I can see their reasoning, BUT a shit update had the app putting an impenetrable overlay on top of the pin screen, and the power off menu too once i activated that.
Took a couple of occurrences to identify the cause - and remove the app, but the immediate fix was ripping out the battery.
This is just an example why users need an absolute hardware kill option - and how they work.
The panic button is a second rate solution which sounds like it wont even be implemented by most suppliers.