We stayed at John's apartment for 3 nights, and enjoyed our time there. The apartment is clean, and reminded us of a junior suite in a hotel. The location was great, on the outer edge of Condesa. I'm used to walking everywhere in NYC so I didn't mind the 15 min walk to Parque Mexico.
It felt like we stayed in a hotel full of junior suites. It seems like John manages the whole building and rents out all of the apartments. There is a common area downstairs, and apparently a nice rooftop (my sister went). There is also a 24 hour reception. Pam, who works the desk during the day, is super friendly and very helpful! She speaks English (which was a plus for us) as well as Spanish and German.
The only traveler tips I would share are: We went in December so the room was freezing (Mexico doesn't really have heating since it's usually warm); I would bring some extra sweaters and socks! Also, the gas for the hot water kept turning off so we had to turn it back on every time we used the water -- but it might only be this unit, and we let John know for him to look into.