The flat is in a superb location -- many of Lisbon's attractions are within walking distance -- it is well-equipped and squeaky clean when we arrived. It appears to have been recently refurbished to a good standard, and is on the fifth floor of a building that feels to be professionally managed.
These positive points were somewhat obscured by a few aspects that are not apparent altogether from the description above, and by a sequence of unfortunate events.
The flat window faces a narrow alleyway, and the neighbour's window feels to be at arm's length. Noise from the street can be clearly heard -- someone playing a guitar, drunk bypassers, an occasional very loud music, particularly on Friday and Saturday nights, but also on weekdays. The insulation and double glazing works fairly well but do expect to sleep with windows closed and air conditioning on.
We faced a sequence of unfortunate events. The lift broke twice, and the dishwasher was not functioning during our week-long stay. These are in principle outside of the hosts' control -- things malfunction at times and the hosts are not immediately to blame. I would however expect them to proactively seek to mitigate those unexpected issues that arose. For example, the hosts indeed brought extra detergent to make up for the loss of the dishwasher -- but after I asked them to do so. It would be nice to have a more clear communication regarding the statuses of the repairs. I sent a couple of reminders to get more visibility on the progress, if any.
The hosts indeed offered an extra night as compensation. That is an immaterial offer given that airplane tickets can't usually be easily amended (and the hosts' knew we were flying).