It's impossible to overstate how great this place is: the apartment itself is spic-and-span spotless. Location is ideal for exploring Lisbon; the Alfama is a romantic place of cobblestones, churches and cafes. The Castelo de Sao Jorge is close by, as is the downtown area.
Sarah (I didn't meet Pedro) is an exemplary host. She is immensely capable, responsive and is a font of insider information on Lisbon and surrounding areas. Dpn't hesitate to ask her for recommendations on places to visit.
If you're looking at staying in the Alfama area, book this apartment ASAP.