My mother-in-law and I had a great stay in Montserrat's apartment for seven days in September. Everything was excellent!
The apartment is very new, modernly furnished and clean, very bright and sunny (close the curtains and you'll have a dark ambience). It is exactly as shown in the pictures, though it feels bigger when you're there.
It's a great location in Zona Rosa, a few Mexican Pesos by Uber away from the Zócalo, from Coyoacán and other areas of interest in Mexico City. The area is very lively at night, but the apartment is incredibly quiet once you close the windows. There are many restaurants and shops in the area (try El Toño just a block or two away, it serves great Mexican food!)
It didn't get hot in the apartment, even though it was the end of summer, so I think no one would miss an air conditioner. Wifi connection worked very well, fast speed.
The refrigerator is small (big enough for a few days, but it might be small if you're staying longer and with more people). Worked just fine for the tow of us.
Montserrat was very nice and promptly wrote back before we arrived. While we were staying there, she even contacted us to know if anything was needed. We didn't get to meet her personally, but she was very kind from before the reservation was made till after we left.
I definitely recommend staying there.