We really enjoyed staying at Borja and Arnaldo's place. The location is perfect - we ended up not needing our metro pass except to get to and from the airport, so keep that in mind! Even walking to the Reina Sofia and Retiro only took about 20 minutes.
The little balcony is adorable and great for people watching. All aspects of the apartment are functional as expected - sinks work, air conditioning and heating work, shower is good, etc. There was even some shampoo and body wash in the shower for us when we arrived! It's very clear our host went out of the way to make us feel at home.
I would definitely book here again!