We had a great stay at Kat's place in Principe Real. Communication was great beforehand, and the apartment itself has everything you might need.
The apartment is in a great location with many coffee shops, bars and restaurants nearby, and walking distance to just about everywhere in central Lisbon, though lovely and quiet at night. It's quite open plan so best suited for a couple.
Kat wasn't available for check in but sent her lovely friend Tina, who was very helpful and even arranged a late checkout for us on the Sunday, after finding out we had an evening flight. Highly recommended.