We stayed in Marlene’s apartment for 4 nights and it was fantastic. It was very clean, and we felt very safe and secure with the kind security guards at the reception of the building. It was close to Zocalo, and to Girabaldi Square with lots of restaurants (we recommend eating at Los Monchis; very good price and really yum food). As is mentioned below, the neighbours are quite loud and the walls thin, so bring earplugs, and the blinds are not blackout, so if you’re sensitive to light in the morning, bring an eye mask.
The only small things that could be improved are that the apartment could use a fan or air conditioning and a little more toilet paper. Otherwise it was a really clean, lovely and safe stay in Mexico City for my sister and I.