I stayed for a week and it was perfect: the apartment is cute, the view across several gardens is wonderful, bath & kitchen have quite new appliances. Herberto is a kind and generous host, he made arriving and checking out easy and comfortable (he was there in person both times). Bonus points for letting me leave my luggage during check-out day!
If you plan on cooking, bring the basics. Be prepared for a very steep hallway.
The location is ideal for exploring Lisboa on foot, but also close to Metro and Tram, and easy to reach from the airport. Small supermarkets are nearby, as well as great coffee. I would absolutely stay there again!