No one seems to have mentioned the main use of the NDB (The ground station cost about half-a-crown a week to maintain) It is ideal for situational awareness during the initial approach phase, ie if the radar controller has forgotton about you, which I've experienced a few times, or just knowing where you are at a glance during prolonged radar vectoring, especially when adjacent to lumps of rock. It helps to keep the flight deck in contol. When STN ditched the SAN, it wasn't long before pilot pressure had an NDB reinstated.