The reason this is a constant succession is that there is NO common definition of "flush".

You can have a reservoir of ZF fluid, and passively permit the trans to pull in new fluid and expel old fluid...OR you can attached a machine that forces non-ZF fluid through the trans. Both may be called 'a flush', but are vastly different.

Then you have mechanics that have made up their mind on 'who knows what definition of 'flush'... perhaps based on experience from tranny shops using powered machines or what not... the 'flush horror stories usually involve some level of 'not doing it right'... people wait until there are shift issues, then get a flush...or a shop does it wrong..or it is the famous Acura/Honda POS trans that the manufacturer blamed everything but themselves for the issues.

So like OE versus OEM versus aftermarket...nobody is using the same definition- it is impossible to have a rational discussion

IMO