Isabel was incredibly responsive and accommodating to make our stay as easy as possible. The kitchen is dreamy and well stocked with the basics if you want to stay in for a nice breakfast or dinner (we wish we had known about the nearby supermarket from the first day - Sumesa!). We also got take-out a couple of times and it was easy to walk somewhere to pick up or get food delivered.
The stairs are no joke, although we anticipated this based on the description. The three flights up were okay after we got our luggage up the first day, just be prepared if you have a lot of stuff you are bringing in/out on a regular basis (we had a stroller). The stairs in the apartment itself are rather narrow and steep.
Overall it felt safe, clean and quiet, especially because Isabel was available for any questions or concerns. Would recommend for an affordable and comfortable stay in Mexico City.