Karla's apartment is located in the best part of la Condesa, so you'll be surrounded by the some of the best restaurants and bars in the city. You're also super close to two nice parks and not even that far away from the historic city center.
You'll get a workout walking up the stairs (multiple times) everyday, but that's probably a good thing. Karla's dad, Carlos, is often around the pollería by the entrance, but don't worry, he's nicer than Gustavo Fring. If you're American he'll probably ask you about your favorite (American) football team as well, so be prepared.
One possible downside is that there's no great place in the apartment to sit and do work (I ended up using a silverware container to rest my computer on as I sat on a bar-stool height chair), but I suppose that's just more incentive to go out to one of the great cafés that'll be really close!