Great location! We really enjoyed our stay here, the apartment is very homey and clean. The kitchenette is great, we were able to cook breakfast each day. The beds were comfortable and the linens were fresh. Street noise is moderate, but I think that is standard for the area. I was slightly worried about not having AC, but Lisbon gets very cool at night and the apartment is well ventilated with the windows open, we all slept with blankets every night!
One thing to note is to take very seriously the comments in the other reviews about the steepness of the stairs (both leading up to the apartment and in the actual apartment). My parents are in their 50s and definitely struggled with the narrowness and steepness, and also with the limited space in the bathroom (toilet is only a few inches from the shower, I sat on it sideways to keep my knees from hitting the shower and I'm only 5'4'').
It's a lovely place to stay, perfect location in Alfama and the hosts we're really friendly and we had great communication with them, but if anyone in your group is very young, elderly, overweight, has knee problems, etc, I would recommend a different apartment.