We had a lovely stay at Paola's apartment. The location was absolutely perfect – within walking distance of everything in the historic centre and around the corner from a metro station and bus stops.
The apartment itself was very large and clean, and had plenty of space for the four of us. The check-in process was straightforward, and there building has 24-hour security who made us feel safe.
One downside is that we found there was a lot of noise outside on weekend nights. This is understandable in a big city, but it's worth noting that one of the bedrooms was quite loud well into the early hours.
It's a perfect base from which to explore Mexico City. However, it might be less appropriate if you want to spend time in the apartment as it wasn't well equipped for even minimal food preparation (e.g. there is no kettle and barely any cutlery).
Overall, we had an excellent stay and I would recommend this apartment to anyone looking to explore the historic centre of Mexico City.