Alline's apartment is a really good budget option. The location is perfect: it's only one block from Copacabana beach (you really can see, and hear, it from the window). The neighborhood feels safe, even after sunset; there's normally a police car stationed half a block away. And a doorman is there guarding the door 24/7 (there are also two adorable door-cats guarding the lobby). Everything you need is nearby: there are dozens of supermarkets, pharmacies, restaurants, cafes, and little shops within a block (the delicious Cervantes steak sandwich shop is just 2 blocks away on Rua Barata Ribeiro, and you can get your morning coffee and pastries half a block away at Boulangerie Guerin). Another bonus convenience: the shuttle bus service which takes you to the Cristo Redentor is right next door, in the Praça do Lido.
We never met Alline or her mother Giselle (who handles most of the day-to-day stuff), but check-in and check-out were easy nonetheless. The key was waiting for us with the doorman when we arrived. Giselle always answered my questions within 10 minutes whenever I emailed her (and I had A LOT of questions), and she was there to give really detailed advice and instructions, all in English. In that respect, she's probably one of the better hosts I've interacted with (and I've stayed in nearly 20 airbnbs).
The apartment itself is nice. The living space is comfortable (it looks a little better in real life than it does in the pictures). The bed is soft and comfortable and the wifi works well (although it's not strong enough for Netflix). The kitchen is basic, and we didn't use it that much, but it seems to have everything you'd need. There's also a washing machine, although we didn't use it. The only downside is that the bathroom can get a little stinky (there isn't a lot of air circulation and Rio can get humid). But this is a budget option, so you shouldn't expect it to be like the Ritz. Overall, you get very good value for the price.