This stay was a mixed bag of pros and cons but I wouldn't stay here again.
Starting with the positives:
João is a very nice person and accommodating host. He was very easy to reach and replied promptly.
The location of the apartment is central so it's easy to get to loads of places.
We were surprised by how big it is! You can fit a lot of people in. The layout doesn't make the best use of all this space though.
Now the negatives:
The area is dodgy, to say the least. The building is located on a narrow street and is used for drug dealing. Always use the upper side of the alley to access the entrance. One day I entered the alley by the lower side and 3 drug dealers accosted me and didn't want to let me through. In the end, nothing happened but no one wants to stay in a street like this. You can see them there day and night.
Overall the vibe of the area is pretty bad. It has plenty of old and derelict buildings and small corner shops. Also walking around at night the streets are dark and deserted, with the occasional tourist that walks past or delivery cyclist. Again nothing happened and I wouldn't say it's dangerous but it's something to keep in mind. It's also worth noting I visited Lisbon in January so there are fewer tourists and it gets dark earlier. If you come in the summer your experience will probably be different.
As other reviewers have mentioned the apartment is older than what it looks in the photos and the furniture is low quality or just old. The entrance of the building has been renovated though. There is also a notice outside this specific apartment seemingly posted by neighbours asking the tourists to be quiet. Also, there is a similar message inside warning the police will be called in case of nuisance. These are minor things but you get the feeling that you're not welcome in the building and the residents are fed up with noisy tourists staying there. This is an old building so the sound insulation is not good which probably explains the noise complaints.
Again because of the age of the apartment is very cold. There were heaters but they were not powerful enough for the size of the rooms.
Lastly, the provided toiletries were insufficient. There was a single almost empty bottle of shower gel. Again not a major thing but it's annoying to have to go find a supermarket to buy these things knowing that we'll only need to use them for 3/4 days.
In summary and as mentioned at the top, there are good things about this apartment but the negatives clearly outweigh the positives. So unless there were no alternatives I wouldn't consider staying here again. There's very little the owner can do about the dodginess of the area but this apartment would benefit from a full renovation including improved heat and sound insulation, and better quality furniture in order to address the issues. I'm surprised the other reviewers had a much better experience than we did so some of this might be explained by the time of the year.