Overall, excellent. I hope to stay here again one day. Tania and Diego are lovely hosts. They always responded quickly when I had questions and even helped me when I got sick one night.
The apartment is very comfortable with a bed, desk, large modern bathroom, large(ish) kitchen, and hardwood floor. Cellular reception is strong inside the apartment and I never ran out of hot water. Lots of closet and storage space, too.
I was there by myself for three weeks, but i could see how two or three people could be comfortable (using the air mattress) for a shorter time. The full-sized bed was comfortable with lots of pillows.
I especially loved the kitchen and balcony. I cook a lot, and found the kitchen to be completely functional, with all the cookware I needed. I ate every meal on the balcony, which has a great view of the neighborhood (5th floor with elevator). Shopping is fun and easy at the local mercado.
The building feels very safe, as does the relatively quiet, middle class neighborhood. It is super easy to get around. Walking distance to Reforma and all the bars and restaurants of del Cuauhtémoc. Right on two Metrobus lines, and close enough to the Metro (subway) for long trips.
Only three negatives: it's dusty--being in Mexico city and having the windows open will mean you have to sweep the floor and wipe the shelves every couple days; the plumbing works, but the drains are slow and the toilet temperamental; the WiFi is spotty and quits every now and then.
Otherwise it's a bright, happy apartment with great "energy" and I highly recommend it.