We had a fabulous time in Lisbon, and Diogo's and Filipa's apartment greatly helped us achieve that goal.
Perhaps the greatest asset is its location - a 5 minute walk to the train/metro station (which also has a pretty good supermarket) and a 3 minute walk from the national pantheon and the flea market. There's also a very nice view from the apartment - be sure to look out the window on sunrise! It was an ideal "base" to visit Lisbon.
The apartment itself is nice and authentic, giving you the feeling of living like a true local. There are three completely separate bedrooms - no need to go through the living room to get to the other rooms. It has a fully equipped kitchen which was very useful. The wifi in that apartment is superb - even when I compare it to places around the world that we visited including in the US. And, at least for us, Diogo said we could actually take the 4G hotspot with us to the city, giving us great connectivity while not eating into our cellular data plan.
Last but not least, Diogo was a great host and waited for us until after midnight as our flight was delayed. He still took the time to acquaint us with the apartment and the surroundings.