Stayed for about 8 days, and it was a great experience. Not only was the host very attentive, but the apartment feels like new, with a very comfortable bed, bathroom and well-equipped kitchen. It is located very close to both Marylebone and Edgware Road stations, which makes travelling across London very easy.
The building itself does not have a lift, so keep that in mind if you are travelling with heavy luggage as the apartment is on the top floor. Also, as with nearly all buildings in London, the place was not built to cope with extreme heat - keep the blinds closed if you are staying during a hot summer or heatwave.
Nonetheless, its great location, quality and host definitely make me recommend it as a great place to stay in London. 10/10.