MATS PT 1 states that the composition of a message should include the full callsign of the adressee and the full callsign of the originator. Once two way comms has been established then there is no need to use the adressee.
I, as a tower controller prefer the 'callsign only' approach, but with the adressee included on first contact. When busy it cuts down on R/T and helps me differentiate between somebody who I have and have not spoken to.
