Javi and Vereniz are great people, nice, accommodating and most importantly the apartment is awesome.
I stayed 17 days and have no complains. This apartment is in the middle of everything! You can walk 25 mins tops in order to get to the mayor sites/restaurants/etc. It is located 2 mins from the train station that has several lines that take you throughout the city. The area is really safe and very quiet.
The room is very confortable and the bathroom is private just beside the room. Both are really clean. There is AC and heating systems so no matter what time of the year you will be comfortable. They allowed me to use the kitchen and the washing machine which helps when you are in a long trip.
I would definitely stay there again when I visit Madrid.