The location of the apartment is its best feature. Located in the heart of Alfama(which is a traditional Portuguese working class neighborhood) it shows you an authentic part of Lisbon in a city thats getting more and more run over by tourists. The apartment is best used as a place not too hang out for extended periods of time, this because the apartment is quite small and there is only a couch that fits two persons(a third or fourth have to sit on a hard chair). I would definitely recommend this apartment if you are exploring the city for a significant part of the day.
Also what is good to know is that, due to the traditional portugues building style of the building the ceilings are low. If you are very tall(190cm+ like me) thats no problem because you are always aware of the possibility that you can hit your head. My "smaller" friends had a bit more problems with this and hit their heads a couple of times. Though the ceilings are low they do not "limit" your freedom of movement.