My experience was more than positive. I found the apartment very clean and fully equipped. The owner is very kind and helpful, moreover she speaks English, Spanish, Portuguese, Italian and maybe other languages. The apartment is just a couple of minutes of walking from the Martin Moniz square where you can take the metro line or take the 28 tram at the beginning of the line, so you can be one of the first people to enter on the tram 28 without finding it already full (which is the normality after two/three stop). Starting from the flat you can also easily reach and cross the city center till the p. do comercio.
The apartment is located nearby to ones of the most recommended restaurant in Lisbon. Some mini-markets are just in front of the apartment. In case of need, supermarkets with more products can be reached in minutes of walking (Pingo Doce and Lidl).
Also in case that you rent car, parking in the evening won't be a mess in that area (I used to park the car in R. Manuel Bento de Sousa where in the evening I used to found immediately empty slots).
Presence of police center and hospital in the proximity make you somehow feel more safer (even if in my opinion the area seems safe itself).