A decent experience overall, with a few problems. The flat is indeed in a great location, very close to El Prado and other museums, Buen Retiro, and bars and restaurants. Konstantinos was a friendly and communicative host (he was out of the country so we didn’t meet him in person, but he was reachable and his friend let us into the flat).
However, there were some issues with the condition of the flat and furnishings, and we’ve suggested to Konstantinos that he should update the photos to more accurately reflect what the flat looks like now. There is no longer a couch in the living room, and several of the other pieces of furniture are broken. Also, two of the stove burners don’t work, and the shower head doesn’t securely fit in its holder on the wall (it actually fell out and hit me on the head while I was showering!).
Konstantinos was very apologetic when we told him about the couch and shower issues—he wasn’t able to address them during our stay, but said he would do so soon.
On a less significant note, the decor has also changed since the photos were taken; there are personal drawings and notes all over the walls. We appreciated that the flat feels like a real home, rather than a sterile empty space. That said, we wished that the photos had better represented the current look of the space, and obviously the repairs need to be taken care of.