Juan wasn't at the apartment during our stay, but if he's anything as helpful and as accurate as Marián was as a host, then you're sure to have a great stay with them both. The apartment is wonderful, very clean and a pleasure to stay in. Marián also struck the perfect balance between being friendly, available and easy to reach but at the same time respecting of our personal space, which we found to be very nice of her.
As far as the location goes, the apartment is at a walking distance from pretty much every major site in Madrid and is very easy to reach from the airport.
Overall, we were very happy with our stay!