Quite edible fresh from my experience..
Actually did a breakfast cook up one time for our fishing club many years ago up at Wathumba creek..
Was a mix of morwong (milf) and trevally..
All filleted, skinned, boned and cooked in flour fresh in the pan and when asked told they were nannagai - we had caught alot of these earlier in the week so helped!
Not one person knew that the fish they were eating was morwong and trevally and there was not a fillet left by the time everyone was done..
Alot of the hardcore guys were a bit the same with regards to their opinion on the eating qualities of morwong and trevally..if only they knew! haha
Oh and if you have ever bought or eaten "mixed reef" fillets from somewhere you have probably eaten it as well