Location is great. If you like to walk, all the sights are within walking distance, but be prepared for lots of up and down but that's Lisbon! Of course there are also lots of busses, trams and the metro in order to get around if desired.
You do need to walk up a few flights of narrow stairs to get to the apartment but if that's not a problem, the apartment is a good choice and the price good for Lisbon.
I would definitely stay again when in Lisbon.