The flat is nice, clean, safe and well located (near the beach, shops and restaurants). It has everything I needed during my stay, and I liked the place very much.
But the best in this flat, of course, is its owners.
Sergio is a very nice and helpful. Even though my flight was changed, and I arrived at 6 AM (not at 7 PM), he not only was in touch all the time during my adventures with airlines and rerouting, but also came and checked me in, which was really kind of him.
Also Ana and Sergio made a great job writing tips and recommendations about Rio, which appeared to be extremely useful, not only if you did not not have much time to dig information by yourself, but in general: nothing can be better than tips from locals.
So, I definitely highly recommend the both, place and the owners.