If you are thinking to visit the city as a tourist, especially for the first time, this apartment is perfect! Exactly in the middle of the central "touristic" area of Madrid, right in the middle between the royal palace (20 min walking west) or El Retiro park (20 min walking east). We never took any public transportation for all the duration of our stay.
Speaking of the apartment itself, it's not perfect as presented. It presents signs of aging and mixes interesting design furniture with others very cheap (f.e. the floor, or the kitchen, with some broken parts).
We had no problem with check-in or check-out.