We stayed in this brilliantly located apartment for 11 nights. It was great to be so central to all the things and neighborhoods we wanted to visit.
We got a deal for our stay, and also a late checkout time which was great.
The bed and pillows felt very firm initially, however we slept very well during our stay.
Alex is a very friendly host with a passion for renovation projects, four wheel drives, acai, and salads from "Bibi."
It was clearly very important to him that we had a great time and enjoyed our stay.
He showed us the many features of the apartment (the most useful of which were the keyless lock and water purifier) in detail, and showed us a few nice places to eat in the area.
Alex bought us some new pots to cook with and glasses to drink from.
In particular, Alex came with us to help set us up with a Brazilian mobile phone, which is quite difficult to get, and took a good two hours. This was definitely above and beyond the call of duty for a host!
Some slight negatives were:
The occasional bad smell from water pipes in the apartment for a few hours. This happened a couple of times late in our stay. However Alex is in the process of putting another Ozone machine in the apartment.
Washing machine not really big enough to take more than a few items at once.
Place is pretty small overall. Fine for short stays though.

The tour we did with Alex ($250USD for two, not including meals) was probably a bit expensive for what it was. Although we should note that we got unlucky with the weather in the afternoon, which definitely affected our experience.

Overall, we really enjoyed our stay and the studio was an ideal base to discover Rio.