Starting off with the location, it couldn't be better located. Roughly 20min taxi ride from the airport (recommended if you don't want to go up the hills of the Bairro Alto with your luggage/bags). Area is extremely safe, even though I wasn't very concerned, either during day or night.
The flat is in walking distance (less than 5min to the closest) from cafes, markets, restaurants and all else needed for either a long or short stay like mine (2 nights). From there we could easily walk to the main areas of the city (I am a walking type, 20km per day easily done in Lisbon) and hitching a taxi ride back there wouldn't take long or cost lots.
The flat itself is well equipped with all you need for staying only a few hours like my friend and I, or if we would like to chill out in there for a little while. Susana & Rita were very responsive, sorted out all we needed extremely fast, provided all tips for the flat and were available at all times to answer our questions.
Definitely recommend the place as I will be coming back there as soon as I can!