The flat is up one flight of stairs in a building on top of a hill. While close to the Martim Moniz metro stop, it is a good-sized hill to get up from either directly (par for the course in Lisbon!). Checkin was easy, and Christophe kindly waited for us as our flight was nearly four hours delayed. Inside, the flat is well furnished, though the living room feels a bit cramped. The beds were comfortable and there is a small room at the end of the hall that was perfect for a crib. Kitchen was well-stocked with coffee and a machine provided, oven, dishwasher, washing machine, and a large refrigerator.
The only real issue for us was sleeping in the warm weather. Since there is no air conditioning, you really want the windows open at night with fans. However, the street is noisy, the street lights are bright, and of course in the summer it doesn't get dark until long after we wanted our children in bed. We were able to get by with the windows mostly closed and the fans on, but it could have been more comfortable.
Overall I'd recommend a stay in Christophe's flat. He was a kind and welcoming host, the flat has some character and is well-furnished, and the location is good for exploring Lisbon.