We stayed at this buhardilla as a couple in May 2018. In short, the apartment and, especially, the hosts was/were absolutly perfect.
The location can hardly be better with easy access to all of central Madrid. Considering the airport is somewhat outside of the city guests should note that it takes around 1-1.5 hours by metro + walking (requires a couple of line changes) or 20-30min by taxi/uber (€25-35).
The apartment, although small, is modern and extremly efficently designed and furnished. It was very clean and functions better than any hotel room considering that other than a double bed + bathroom you also have a little kitchen/living room with a loveseat sized couch that can turn into a single bed. Might be somewhat cramped if travelling more than two people.
The detail that impressed the most was the hospitality and service given by the hosts. We arrived at around midnight and they were patiently waiting for us in the main street to help us find the place and "check-in".
Included in the experience they had a convenient coffee capsule machine and they had stocked the fridge and supplied a breakfast hamper. The final flurish came with a bottle of tasty Spanish red wine and some delicious serrano ham.
Furthermore, throughout the stay Arianna was constantly available through the Airbnb-app if we had any questions concerning the apartment or Madrid (tourism, food&drink, and more).
The price was also second to none for the central location, but regardless of this fact we really can't recommending this place enough. A solid 11 out of 10.