Overall, the flat is very cute, mostly clean, sufficient towels were provided and tastefully decorated, but there were a few major inconveniences.
We stayed for 3 days at the end of December 2021.
Noise/quiet hours: 4/5. I could hear the TV on in the downstairs or upstairs flat every evening until 10 pm or so, even after I got into bed. Early in the morning around 6:30 am, neighborhood ladies could be heard congregating below the windows and chatting on the street. It's a residential neighborhood with small flats in old buildings, so this is standard fare.
Cleanliness: 3.5/5. The bed and towels were clean, but other parts were not at all, making me wonder whether they followed the Clean&Safe Portugal standards. The towel warmer/rack was visibly very dusty and I had to wipe it down before we could hang our towels on it. Two out of the 3 mugs I took out from the cabinet had coffee/tea rings on the inside and some of the glasses looked unwashed/grease-smudged. I tried to find the cleanest cups and rewashed every cup I used before using it. There's a cleaning fee, so I expected it to be cleaned more thoroughly.
Responsiveness: 5/5. Frederico, the owner, sent a warm welcome message initially then handed me off to Alexandra/Pedro, who responded quickly to most inquiries.
Check-in process: 2/5. Check in is btwn 4 pm and 10 pm and they won't allow early check-in. Overall, I wish they could be more flexible and helpful with these procedures for travelers unfamiliar with Lisbon/Portugal.
The next part may be due to Covid regulations and may not apply later, but they required us to fill out the gov't traveller locator info before I left my home country. I understood the necessity of the form 100% as it's a government regulation, but their urgency was hard to understand and added unnecessary stress.
I let them know multiple times that I couldn't complete the form until I met up with my friend in Portugal because I didn't have my friend's passport info and that we hadn't yet solidified our ground transportation to Lisbon from within Portugal (information that the form requires). I assured them MULTIPLE times that it will be completed once we had all the info and definitely before we arrive in Lisbon. I still kept getting messages urging me to do it or that they won't set up check-in to the flat while I was on tours/visiting monuments, adding unnecessary stress. I felt like I was responding to an anxious, demanding client while on vacation.
They eventually told me to do it at least 2 days before I arrived in Lisbon, which was arbitrary, given that the Passenger Locator Form for international arrivals into Portugal submitted to the Portuguese government for Covid-tracking purposes does not need to be completed until just before boarding the flight, and our other accommodations in Portugal didn't require passport info until the moment we checked in.
NB: There is a person-to-person key hand-off, so they require you to give the exact time of arrival at the flat and any changes to your schedule requires 2-hour advance notice. Isabel met us at the flat and she was friendly. She showed us around, told to make sure we locked both the front door and the building door when we went out and her only check-out instructions to us were to leave the key in the bowl in the kitchen when we left.
Check-out: 5/5. We checked out a day earlier so we could be closer to the city center and airport on our last day in Lisbon. I messaged Alexandra/Pedro in the morning that we'll be out by noon and left the key in the bowl like Isabel said. I messaged again after we left.
THINGS THAT DID NOT WORK IN THE FLAT:
1. The door to the smaller of the 2 bedrooms doesn't latch shut, letting warm air out into the rest of the apartment.
2. The shower stall is so small that the water splashes out onto the rest of the platform where the toilet and shower are located. Particularly because when the water is first turned on, water comes out of the hand-held shower head that is angled to spray directly forward and out of the shower tray. The bathmat was completely drenched by the end of a shower and would not dry during the day even when I tried squeezing out the water and laying it flat.

3. Hot water runs out in 10 mins. I didn't know this and on the 2nd night I took a 15 min shower (slightly longer than the first night) and the last 5 mins was in ice cold water, in December, in a flat without heat. It's a good thing my friend showered in the mornings because there's no way 2 people could shower one after the other. She also said near the end of a regular 10-min shower the water was getting cooler and cooler.
4. The Biggest Inconvenience: within 15 mins of being in the apartment after Isabel left, the lights went out.
There were 3 space heaters provided in the apartment, and we turned on 2 of the smaller ones to warm up the bedrooms before sleeping, and the electricity went out almost instantly. We were unpacking in our respective rooms and spooked. After several back-and-forth texts with Alexandra/Pedro and providing photos of the fuse boxes (in the mirrored closet by the front door) and photos of the outside street and stairwell lights to show that it's not a street-wide outage, we found the correct fuse to flip back to get light back.
So in reality, only 2 of the smaller heaters could be used at low/medium power. We didn't even dare think of touching the large space heater in the living room and didn't use that space. We closed all the shutters in the evening and opened them in the morning to try to use solar heat to our advantage.