We enjoyed our stay at Rui & Elsa's place. The flat is located on the edge of the old town, which means its quiet but takes some walking to get into the middle of the action. The flat was clean and quite spacious for 2 people. Communication and check-in were all good via Whatsapp.
The only thing to note (if you're not familiar with Lisbon) is that if you're looking to cover Lisbon by foot be prepared because although the center does not seem to be far, its steep up and down hills all the way!