I have stayed in many places in Madrid. The thing I like most about this place is the lovely terrace. It lets you enjoy the mid day sun, the evening breeze, a sounds of the city, all from your own little private piece of the Madrid skyline.
The location of the apartment is very central. It is close to the subway. It is near the major attractions. Very walkable.
I think it is perfect for one or two people. Since the bathroom is upstairs with the bedroom it might be a little inconveniente for more than two people (someone on the sofa for example). Also, the bathrooms ceiling is a little low if you are tall, but the height in the shower was comfortable.
I really enjoyed my stay there and would stay there again in the future.