Sergio was very responsive. Before we even arrived, he sent us lots of useful information on the apartment. Sergio was not in the city when we arrived, so he had Betty meet us at the apartment. She spent time showing us how everything worked, and she gave us her number just in case we needed anything. Sergio checked in with us during the trip and let us know if we need anything to let him know. I did need something and not only did Sergio respond right away, but he had Betty deliver it to the apartment in just a few hours after we asked!
As far as the apartment goes it is just as shown in the pictures and very comfortable. As others have noted it is on a busy street so you will hear noise, this was not an issue for me since I live in a busy city as well, but something to be aware of. There are several grocery stores very close to the apartment. There is a small one directly across the street and I walked past about 4 others in just a couple blocks. The metro is only a block away. It is very easy to use and super cheap. If you chose to use a taxi there is a taxi stand right across the street but since the metro was so convenient we chose to use that.
If you plan on taking tours from the tour operator Tangol this is a great location to be in. Their main office is about a 10 min walk from Sergio’s apartment. The Teatro de Colon is a little over a mile away and Plaza de Mayo is even closer. Overall the apartment was great, the location was great and Sergio was a great host.