Well they were called Stansted approach which gives the game away.
Low level they may provide you with a service around Stansted, City, and Biggin and will handle IFR approaches to these.
The service provided is always excellent but their capacity is often stretched.
Southend "overlap" with their LARS service and are often a better bet low level but their coverage is often poor south west of the Thames due to the location of their head and lack of a direct feed from NATS.