Apt 505 was our "home" of sorts during our 5 day stay in Mexico. As soon as we booked, Alice was in touch with us offering helpful tips and very detailed instructions on how to get there and check-in procedures. We found the entrance to the building very easily, but I can see how some previous guests could have missed it, especially if you arrived late in the evening when it was dark, as the entrance and the surrounding wall are both white. Just follow the hosts instructions and you will be able to locate the door pretty easily.
The location is very central and close to many of the popular sightseeing options (walking distance to Palacio Nacional, the Cathedral, Temple de Mayor). If you have any concerns about safety you can rest at ease- this place is very very secure and safe. Angel the Doorman is amazing and very helpful.
Inside we had all the amenities we wanted- kitchen utensils, hot water, towels etc. Alice had come by to check in on us in person (as we met only the doorman when we arrived) but we were out most of the day everyday and we missed her. But she was very accessible via chat and phone. After check out at 11 we were able to securely leave our bags with the doorman while we walked around, as our flight was later in the evening.
The only thing I would note is the noise level from the streets. Its just one of the downsides of being so centrally located in the area. There were a few nights where we did wake up due to a loud car alarm going off, or the phone of a neighboring apartment ringing in the middle of the night or car noises. But being located downtown close to the sightseeing places was important to us so we did not mind the noise too much.
So if you are light sleeper I would suggest checking out some of the other apartments hosted by these folks.
All in all for the price it was very worth it! I would definitely stay with these wonderful people again when I visit Mexico City.