We just spent a week at Joana & Dudu's place and were pleased with our stay. It is sized well for two people, and is in a great location, with a miradouro just two short blocks away. Time Out Market and the train station to Sintra are walkable from here as well. The street is quiet enough to get plenty of rest at night, with some light daytime foot traffic.
We communicated with Joana a few times during our stay, and she was responsive and helpful each time. My only advice for this place is, if staying during the winter, make sure to bring warm PJ's just in case. This was nothing Joana could control- the weather was especially chilly for Portugal during our stay- but since the balcony has glass doors, the front room of the apartment was hard to keep warm even with the space heaters provided. That's my only heads up though, this apartment is a good choice!