Many towers have had what is now called an 'Aerodrome Traffic Monitor' (ATM), formerly 'Distance From Touchdown Indicator' (DFTI) for over 40 years. Uses are strictly limited to monitoring spacing on final approach and position of visual circuit traffic, however controllers with ADI and APS ratings are not permitted to vector traffic using it, but they may pass generic traffic information derived from it, so it's not a new system being trialled.