Your screen has to be fixed to something that will not disintegrate under its weight. All flush mount brackets are kind of similar in "flushness"... Also, the input sockets are normally at the back off the TV, so you need some space.
I know someone who chased 150mm into the wall so that the tv sits flush,mounted on a bracket.
He then clipped an aluminium frame around it to give it that effect.
He even chased below it for wires to run.
Looks neat but pretty pointless imo