We had a great stay in Helena's apartment which is within a very new, modern building which includes all of the things you might expect (facilities in excellent condition, elevator, etc), so it was really awesome.
One thing to note is the noise coming from outside at times. We very well knew it was Bairro Alto, and that the neighborhood is "lively" but at times it was rough, especially when the construction started in an apartment across the street — which is in the level of Helena's apartment, but most of it was going on during the day while we were outside. It's not a huge issue, especially if you don't mind sleeping with the windows closed, as that completely solved the problem for us, but it's something to consider if you are planning on getting quality rest time.