If you don't mind stairs and don't have young children, book this place immediately. Our family (with older children) had a wonderful week in London here.
The flat is perfect because:
Space--the main floor is full of light (3 skylights) and stylishly decorated with a fully-stocked kitchen (including washer/dryer), the bedrooms are one floor below (good for privacy), there is an updated bathroom w/ a small sitting area outside its window (shielded from the wind in case the roof garden is too cold), and WOW!, an amazing private roof garden with 360 degree views. It was unusually warm during part of our week there, but the bedrooms were still cool, there was a good fan for the main floor, and there was always a breeze on the roof. The internet is fast and strong, w/ 2 different routers.
Location--It's on the Victoria line (frequent trains) 4 minutes from the Pimlico stop and 12 minutes from Victoria station. The #24 bus stops 50 feet from the front door and goes to many of the sights (Westminster, Buckingham Palace, British Museum). It's also easy to walk to the Thames and many tourist sights. Pimlico is a safe, charming neighborhood with great restaurants and pubs, although we ordered or cooked in most nights so we could watch the sunset from the roof garden.
Hosts--they responded quickly and completely, and were very accommodating with our check-in and out times. They provide great advice in the house manual and neighborhood guide. They also stock the flat with all necessities, including toiletries, tea & spices, and games to play on the roof (we loved the drinking Jenga game and travel Scrabble). Our vacation was much more memorable because of this charming flat--I would highly recommend it!