Sérgio is a wonderful host! He was able to pick us up from the airport, showed us around the apartment, and while we were there, he sent many tips and invited us to lunch as well. It was like having a good friend in Lisbon! Plus, like many other reviewers mentioned, he gives you a personal wifi hotspot so you can take that with you around the city, which is very helpful. Inside the apartment, the signal isn't always great, but it worked well most of the time.
The apartment is a good size for 2 people and is well equipped (washer, iron and board, hairdryer, a few electric plug strips throughout, and even a microwave in the dining room). The bed was comfortable too. It's a pretty quiet neighborhood except in January when we visited, there's construction going on that you can hear starting early on weekdays and at night, pretty much like clockwork, around 1 am, there are either the garbage guys or guys coming out of the bars/restaurants, but it actually wasn't terrible even though I'm a light sleeper.
The apartment is right in the heart of Alfama and just down the hill from the Castle. Barrio Alto and Baixa are only about a 15 minute walk away but if you like to be a little more central, this can be a little less convenient. But if you want a little bit quieter of a neighborhood, this is a good choice.
Only 2 things to note, if you're sleeping upstairs, the bathroom is a little far away at night (down the stairs) and the short ceiling is definitely a factor both upstairs and in the dining room. My husband and I both bumped our heads a couple of times (and I'm only 5'2"), but the rest of the place is great and Sérgio is awesome so we whole-heartedly recommend this place!