We enjoyed our stay Sara's flat! We are a family of 5 from Atlanta, kids are 14, 12 and 10, and we stayed a week. The flat is located south of Earl's Court station, which is on the District and Piccadilly lines. The Piccadilly line serves Heathrow, so it is a very convenient 45 min tube ride from the airport. Earl's Court was an easy tube ride anywhere. There are many shops and restaurants near the station - M&S Foodhall, Tesco Express, Boots, Starbucks, many chains like Wagamama, Zizzi, Pret a Manger, plus many pubs and burger, Mediterranean, pizza joints.
The flat itself had everything we needed. The beds were comfortable. As others have said, the living room is noisy from the street traffic, so if you plan to use the sofabed in there and are sensitive to noise, you may consider earplugs and eyemask too, as the blinds in there are white and the room gets pretty bright. There is no AC but we just opened windows and used fans to cool the flat. It was chilly at night and we spent most of our days seeing the sights, so we had no problems with it being too hot, even though we were there in June/July.