Casa 48 is an absolutely wonderful place to stay. The facilities are clean and well-maintained. And yes, the views of Botafogo Bay and Pão Açucar are indeed spectacular.
Perhaps most importantly, Valentin was a gracious host who went above and beyond explaining the dynamics of different neighborhoods in Rio and making informed suggestions about what to see/hear/eat. I am very thankful for heeding his advice.
A note about the location: Santa Teresa proper is a fantastic neighborhood. There are many bars and nice places to eat within a 15 minute walk. With regards to the favela adjacent to the house, I found the airbnb listing information to be accurate. I walked through several times and felt completely safe.