My husband and I stayed at Guillermo's place for 4 nights and we really enjoyed our stay. The location was great with cafes and bars within walking distance.
It was also very quiet based on how central it was. Across the street there was a Bici Mad city bike pick-up/drop-off location and we used those bikes to ride all over Madrid, which we loved. What we didn't love was the uncomfortable couch and the dingy kitchen with dirty walls and plates/pots/utensils that looked like they were purchased at a garage sale.