Francisco and Valeria are excellent hosts and will go to great lengths to make your stay more comfortable. They were easy to reach at any time and any small issue that might have arisen was dealt with promptly and effectively.
The apartment is fair-sized, well equipped, quiet and very central for such a reasonable price. I personally walked everywhere during my week long stay. Even Palacio Real is within a 10-15 minute walk if you have good legs.
But really you do not have to go anywhere.
The area is very lively day and night with lots of markets, shops, restaurants, bars and terraces to mingle with the locals. And you always have the chance to cook something in the apartment if you prefer to save a little.
Whenever I fly back to Madrid in the future I will most definitely try to book their cute apartment again.