Well let me start out by saying I have believed in flushing.
I think the basic theory behind it is sound, deny the pant nutrients at the end of flowering so it consumes itself and thus leaves you a higher concentration of plant to product ratio. All that greenery has choraphil and minerals in it.
I’m no biochemist though.
Here is a research paper that has said to proven flushing is pointless, although unfortunately this is the only study done to date that I can find.
I wonder what a larger scale study that included a flushing agent vs water flushing vs control would ultimately show.