We spent 2 nights at Sergio's place and we had the greatest time. He was a very kind guest and promptly reacted to our request of an earlier check in - and when we texted him that we had arrived more than one hour earlier that we thought, he quickly came to meet us and let us in. He's been extraordinarly reactive during our whole stay.
The apartment itself is great value for money: cosy and comfortable, not to mention that it is astonishingly quiet if you consider that it is in a very central area at a few minutes walk from some of the most important touristic sites (Prado and Reina Sofia museums, Lavapiés neighbourhood, Buen Retiro Park, Plaza Mayor etc.). The bed is comfortable and the bathroom is small but ok, with a nice hot shower. It is very close to a metro station (2 minutes walk) and to Atocha train station (5 minutes walk - connections to the airport via train and bus). It was not the first time we were in Madrid, but for but of us it was the first time we stayed in such a good and central location at such a reasonable price!