Nelson's apartment is in a great location in Lisbon. Close to the metro station, and with plenty of shops nearby. It's a great base for exploring the city, and clean and comfortable inside.
As other reviewers have mentioned, it is a lively area, so the streets can be noisy - if you bring a good pair of earplugs though, this drowns it out.
Noises from the flat above do come down, and often sounded like someone was trying to get in the door of the apartment, which was really unsettling at night and being by myself.
Overall though, the apartment is clean, cosy and the location is excellent. Nelson was also super helpful, and communicative.