This is a fantastic find for a trip to Lisbon. The tl;dr if you're trying to decide on this one is that there are a LOT of stairs, and a couple very small things you might find wanting in the space, but if you're looking for an amazing location, and you're there to be in Lisbon and not in your Airbnb, then this is a perfect spot.
Longer Take: This is an excellent find. Lots of beds if you're travelling as a group (though only one key; plan accordingly), and plenty of space to hang out. The skylight windows were a huge plus — great ventilation, fresh air, awesome in a rainstorm. Full kitchen if you want to cook, and two AC units (major plus if you're visiting in the summer). Fair warning that there are a LOT of stairs, but if you're in reasonably good shape at all, this should be no problem; even after a long day and a full dinner, no one in our group of four had any issues at all (though we're all athletes). If you're visiting Lisbon, though, you're gonna be doing a lot of stairs and walking up hills anyways, so this shouldn't bother most people. Some things in the place were a bit lacking (the shower took some finangling, e.g.), but nothing impacted our overall stay. If you're planning on getting this place to stay in a lot, maybe this should weigh more on you (though I still think it's a great option), but if you're going to be out for most of the day, this place will be perfect. The location in the heart of Alfama is excellent. Tons of good restaurants just around the corner, lots of shops, easy walks to pretty much anything you want to see, right next to the church, etc. etc.
Would happily stay here again on a return visit.