This is definitely a nice and very central place in Retiro right at Plaza San Martin. 5 minutes walking distance to Florida. A small supermarket is right across the street. The building is secured by a 24/7 doorman. The area is pretty safe.
The flat is on the 3rd floor (elevator) and was very clean. I had a wonderful sleep on the bed and great showers in the morning with good water pressure.
Unfortunately I did not meet Lucila and /or Guido in person as they were working when I arrived and left. However, everything worked out perfectly fine. Whenever I had a question or needed something Lucila replied very quickly to my requests.
All in all a good and decent place to stay.