Our stay at JP's was great. We are 2 couples and the space was just right for us.
The location was the main highlight - the city is at your front door, and trams etc are all close. (The no 28 yellow tram stops just a few steps away. )
The building is old so don't expect super modern and slick, but this adds to the charm and authenticity of your Lisbon adventure. Also be prepared that there is a flight of stairs to get to the elevator - if you have trouble with stairs this may be difficult for you. The lift is also one of those old, tiny lifts that my friend found a bit claustrophobic- I thought it was fun!
The apartment was clean, beds comfy and we loved the doors/ balconies on all sides. Great air flow. Overall, I'd recommend this as a top place to stay.