I went to Rio with my girlfriend for the Rock in Rio 2013 weekend and our experience in the Nano-Apt was great!

The apartment is really nice decorated, has all you need for a few days in Rio and, the best of all, is EXTREMELY well located. You are in the heart of the best part of Rio, right in middle of the way between the beach and the lake, simply great!
Even the sofa-bed is comfortable enough to spend a few days (you can't "feel" it in the pictures, but I'm about 6'1' and I guarantee it's comfortable enough).

Brunello is very nice also, I completely recommend him as a host, he was on time to receive us in the apartment, showed us how to use everything and left some tips on how to enjoy the city. Even when we got a little eletrical problem in the apt he got to the apt to fix it before we got back "home" again. (yes, I was already calling the place "home"). :)

If you don't mind living in a very small place for a while (I was only there to sleep, so I didn't mind at all), I completely recommend the nano-apt. If you're looking for a bigger place, look at the other apt from Brunello in the same place, you can't pass on this location!