We stayed at Paulo and Patricia's studio for seven nights and had no problems at all. The apartment is safe (there's a doorman 24/7), and it's in a great location (allowing guests to get around easily either on foot or by public transportation).
It is located a few blocks from the Gal. Osório subway station, which gave us easy access to different parts of town and connections.
The hosts were very friendly. They welcomed us with a basket of tropical fruits, bottles of juice and water, and checked up on us regularly to see if we needed anything. We will definitely be back.