A full grip requires significant mobility ーdeveloped if need be over time. The thruster is a combination of a front squat & push press, and requires a transfer of power from lower to upper body. That transfer is best made with a full grip on the bar. Front squatting can build the habit of not keeping a full grip on the bar: we loosen the grip to allow for a higher rack position. This is good for the front squat, but bad for the thruster.