I'm sorry to be the first traveler to leave a mixed review about the flat. Let's start with the positive aspects: it's a quite large flat for Lisbon's standards with all amenities needed for a short stay. The location is excellent if you want to visit on foot the city (but more on it later). The beds were comfortable enough and even though we didn't experience a major heatwave, the flat was not too hot when temperature outside hit 33° (there are multiple windows so it's easy to let the breeze in).
Now to the two main negative aspects (which can be detrimental for the flat appreciation if you are sensitive to these aspects):
1. Though the insulation is quite OK, the sound-proofing is almost non-existent; not because of the windows which can handle low noise but because of the walls which are very thin and the whole building design. I understand it's an old building but I also lived in some of them and I never experienced this absence of sound-proofing. It's manageable during the day even when the funicular works but there's the second drawback...
2. Rua da Bica is a very popular street because of the picturesque view and funicular. I was aware it would draw a crowd of tourists that would walk it down, take pics, drink a coffee outside, etc. What I was NOT expecting is that it basically becomes a public drinking area with bars blasting music up until very late during weekends (also on Sunday) and patrons shouting, which combined with the lack of sound-proofing makes sleeping, even with earplugs, a difficult task. The single bedroom is street-facing so you basically hear anything that happens outside.
Last but not least, I'd like to point out that I reached out to Nelson because we also had loud neighbours upstairs and they stopped after he messaged them. I appreciated it and wanted to point out that he made the effort to lower our noise issues.
All in all, I'd only recommend this flat to people who are willing to party in Lisbon because you'd then have less trouble sleeping after a night-out and could enjoy the lively and busy Rua da Bica by night. This was unfortunately not my intention but to each their own.