Sergio was gracious, friendly and helpful from before I even flew to Madrid for this last minute work-play trip.
He offered to pick me up from the airport for less than what a taxi would charge and came to do so. I didn't have a cell plan to use while in Madrid but he was flexible and we were able to communicate via email/my laptop. He was very responsive to any questions I had trying to figure things out in the apartment or whatnot.
The loft was cozy and well-located to walk to many sites in Madrid. The Reina Sofia museum was just a 10 min walk away. The building was quiet and I never heard noise from outside in the flat. Fyi, it is up 4 floors so be prepared for some stairs to get up there if you have a lot of luggage. There's a supermarket just around the corner which was convenient for getting snack items or if you wanted to cook. The neighborhood felt safe even after dark.
All in all, a fantastic deal for central Madrid and a very nice host!