We had a great time in David's apartment. It's spacious and modern (with a really good rain shower -- always a winner for us!). It also has good WiFi, air-conditioning, and everything else we needed (with the washing machine a useful bonus).
We didn't meet David personally, but check-in was painless thanks to his assistant Edita (very friendly despite the language barrier!), and he was kindly in contact with us on AirBNB throughout our stay.
The location suited us well, as it's 5 minutes' walk from Cava Baja, justly described as the best tapas street in Madrid, and within walking distance of, but not too close to, the main tourist areas. The apartment might be better for younger or more "adventurous" travellers, because of its neighbourhood (fair amount going on at night, lots of hipsters, etc), three flights of stairs without an elevator, and the fact that it's the opposite side of central Madrid from the Prado. For some people, those might be drawbacks. For everyone else, I recommend David's apartment!