My girlfriend and I enjoyed staying at Rui & Elsa's place for a few days while we visited Lisbon. The flat was ideally located near Rossio sq, very central and ideal for exploring the historic centre of the city on foot. Other than its location, we also really liked how cozy the apartment was and, despite being pretty small, it had everything we needed for a nice stay.
The only downside we found is that there was a strong smell of sewage coming from the shower drain, which the hosts seemed to be aware of. This wasn't a big problem for us as it didn't reach the bedroom.
Overall, we enjoyed our stay and we'd stay here again.