Sergio is a wonderful host and easily available. As a family with two young boys, the apartment set up and location worked well for us. The apartment was warm enough (despite previous reviews suggesting it was cool... Maybe coming from cold, wet England we were more acclimatised...).
At first thought (never having been to Madrid) we weren't sure about the area, but it was perfectly safe and only two small blocks from the metro. There is a small convenience store located around the corner - a lovely couple selling fruit and veggies and other basics.
Good amenities - bathroom, kitchen etc and wifi.
I personally found it a bit noisy in the mornings as shop keepers opened their sliding security doors, and local street and garage cleaning but I expect this happens everywhere so close to the centre of the city. It was not an issue from the main bedroom and the kids slept through everything anyway.
All up - a great stay and we would stay here again based on price, location.
A word of warning - it is two flights up so if you have heavy suitcases you need to be aware.