The apartment is perfect for a couple and good enough for 3 to 4 people.
The location is perfect to visit different parts of Lisbon. (Train to Sintra at <5mins away / Ferry and train to Cascais is also relatively close +- 10-15 mins by foot)
Finally, the apartment is well equipped, warm water works well and fast and the kitchen has most of the things you need to experience Lisbon as a tourist.
The ceiling in the mezzanine is not that high, so, personally, we didn't use it a lot.