Ideal for east London. Not sure what transport links are like at Southend airport, but trains from Southend to east London are very regular, 4 an hour from memory?.
The airport is pretty well served from east London. Three per hour from Liverpool Street, Stratford and Shenfield and one from Romford.
Though of course all four of those have a very frequent and fast service to Paddington via the Elizabeth Line nowadays. Plus the service to Newquay is set to double in frequency from May.