Well equipped apartment that is centrally located. We really enjoyed its proximity to many major sites, the castle, Alfama and transportation. Apartment is clean and the windows do a very good job of keeping the apartment quiet as the area can be quite noisy. There is construction next door and the work (and noise) generally stops around 6pm.
Check in was a breeze; after completing some necessary forms online, a passcode is provided which allows access to the building and your apartment.
The hosts were very responsive and we appreciated the ability to store our luggage for several hours after check out when our flight was delayed.
Note that the floors squeak a little and transmit sounds directly to the units below. It can be bothersome if the upstairs neighbours are heavy footed (which happened one night). Wifi could be improved: it had intermittent instability - annoying but manageable.
On balance, a very good stay in apartment 5.1 with excellent hosts.