This is a special place, which I recommend for couples with intimacy or close friends. My husband and me stayed there for a whole week. Bairro Norte can be noisy especially during weekend's evenings, but this did not disturb us, since the apartment is relatively silent.
Nuno is a very nice guy, always willing to help. We had arranged to get into his apartment early in the morning, since we would land in Lisbon at 6:30 AM. Just before our flight, I sent him a message and was told this would no longer not be possible and we would have to check in later, after 1 PM. I got disappointed but he said he would help us with the luggage. So he did. Early in the morning there he was, at Praça do Principe Real, waiting for us. He took our luggage to his place. Some hours later, he helped us to bring them upstairs to the apartment, where he kindly left us a bottle of Douro wine. By the way, the place is on the 4th ground and the stairs are really tiny - this can cause some difficulties, which are overcome by the many advantages of the place. The highlight is definitely the wonderful view on the rooftop.