We stayed in that flat for 3 weeks during covid times in winter, our stay was mostly quite nice and comfortable, the area in particular is great with Estrela just nearby. The terrace is spacious though gets little sun. That is probably welcome in the heat of summer though! The small kitchen has the essentials with a few pots and pans and utensils, enough to cook occasionally. We didn’t meet the owners but they were very responsive on WhatsApp.
There are two minor elements that we didn’t like so much, one is that the apartment can get quite humid, towels won’t dry in the bathrooms for instance, and it can smell a bit as a result. Another note is that a few things were partially broken: the blinds in the rooms, the door handle to the terrace, and the front door lock gets stuck half the times and cannot be locked fully.
These are all minor points, fairly easy to fix though, overall we’d still recommend this flat for a few days in Lisbon discovering the city!