My fiancé and I loved our time in this Bairro Alto flat! It was spotlessly clean, had gorgeous natural light inside and unparalleled views from the rooftop terrace, which we took ample advantage of. Additionally our hosts were amazingly accommodating regarding our check-in and check-out, which had been one of our biggest concerns since we were arriving and leaving Lisbon hours before/after the official times and had no idea what to do with our luggage in the meantime. The area is extremely walkable (if you don't mind hills, but that's the whole city!) and we enjoyed every minute of our time in Lisbon with this BnB as our home base.
My only notes (and I wouldn't consider them negative, just something to keep mind) are that 1) it somehow failed to dawn on me that a flat with a rooftop terrace would necessarily have to be on the top floor, so be prepared to climb some stairs and perhaps pack light accordingly so you don't have to haul anything heavy to the fourth floor, and 2) there is only one toilet in the flat, and it is not separated from the rest of the rooms in any way like with a door. If you're not travelling alone, you should probably have a high enough level of comfort with your partner that this isn't an issue, or be prepared to spend some extra time up on the terrace anytime someone needs a little privacy to use the facilities.