I stayed in this apartment for 2 months and I totally recommend it! It is only 10-15 min away from downtown, 10 min away from Miradouro da Senhora do Monte, 5 min away from the subway, the grocery store, the pharmacy, the bakery... You can find everything you need nearby. Plus the apartment is fully equipped (the kitchen and the bathroom have everything you need), the bed is comfortable, so it is just perfect for a long stay.
Sometimes there can be some noise on the street late at night (waste trucks do the rounds at night in Lisbon), but it was not a big problem for me. Also, sometimes you do see some people smoking and drinking in the streets, but I have never had any problems with them. The neighbors were very nice and Justus is a great host!