We stayed for two weeks in Ana's flat. It's in a great location, so long as you are ok walking a little. We loved it, far enough out of the tourist areas to have plenty of local places around but still a very quick walk to visit all the sights, etc. Uber is very cheap in Lisbon too, it was only 11 euros to the airport!
There are a couple of things worth noting about the flat that aren't clear in the listing. First, whilst the area is pretty quiet and not too much traffic, it is under the flight path in/out of Lisbon. Great if you are a plane spotter, less so at night!
Secondly, the mezzanine bed does not have a lot of headspace above it. If you are tall, like my partner, it can make for some interesting moves getting in & out. Likewise, with the bed being in the roof space, it does get very warm. The fan is great at cooling it down but only when you aren't trying to sleep as it's very powerful/noisy when running.
Lastly, the flat I guess has been going a while now, as wear and tear is obvious throughout. Ana is extremely responsive to any problems you have, quickly replying and offering to sort them out. Just be aware it's no longer as new/shiny as the photos look.
With all that said - we thoroughly enjoyed our stay. The balcony is such a brilliant addition to the flat - the view is terrific and it gets plenty of sun. There's even a table added now to enjoy eating & drinking outside - which we made the most of for sure!