The posting says "Perfect apartment, perfect location", and it is, in fact, accurate.
Starting from the end: You simply can't beat the location of this one. If you are going as a tourist to Argentina, you will want to stay in San Telmo (because it is the most iconic, vibrant, beautiful, and strategically located neighborhood), and Sergio's place is at the heart of San Telmo.
Then, adding to that, everything else is also perfect: The apartment is beautiful, comfortable (with 3 spacious rooms), clean, quiet, and well equipped.
Finally, Sergio is an outstanding host, always going above and beyond to make us feel welcome, and ready to enjoy our days in Buenos Aires.