I've used this booking site before and Brian and Maria are easily the nicest and most helpful people I've booked with! Very helpful instructions for self check in because of our late flight, and great recommendations for stuff to do on the island.
The apartment is spacious with a balcony at the front and back, nice and cool in the hot weather, and really close to the shops and restaurants on the water front.
Marsaxlokk isn't a main tourist spot (yet) but you've still got a lot of restaurants to choose from, if you like fish the quality of the meals is second to none. The locals are all very friendly, and you're still close to Marsaskala and a short drive from the blue grotto.
Thouroughly recommend!