The location is central and convenient (it is 5 minutes to Lapa's main entertainment area, a 15 mins walk to the seaside museums/piers/entertainment areas of Praça XV de Novembro or Praça Maua, 5 minutes to Saara's market), but the neighborhood is a little gritty and -according to everyone I talked to- not safe to walk alone, especially at night. Having said that, as a female solo traveller I had no problems - just mind your surroundings, don't flash phones, cameras etc and use common sense. Use a taxi in the evening. There is a police station a few meters away on the same road.
There are also a couple of bars just in front of the flat which on some evenings (friday?) play music till 10 or midnight. Challenging for those who have sleeping issues, quite cool otherwise. Mostly samba (and you can watch some very good dancing from your 5th floor window).
A really nice bakery - 5 minutes walk to the left, on the opposite side of the street - sells bread, sweet and savoury pastries, cakes and some hot food. There is also a supermarket next to it.
The hosts were away when I arrived but a (lovely) friend of theirs met me at the flat, and they were very accommodating throughout.