We had a wonderful stay in this apartment in the middle of Alfama. We were received warmly by one of Juan's colleagues and stayed in contact with Juan via chat throughout our vacation.
The pictures are true to the apartment - it is quite roomy for an Alfama apartment which are known to be tiny. Tall paper (>1,80m) might feel a bit crowded in the entrance, but it didn't bother us much. Everything was in order and clean, though you do see that it's not a newly renovated place, so the floors are a bit creaky, the water boiler needs some nudging to produce hot water, and the bathtub has a few stains. But it's all part of the charm of living in an old flat in the old part of the city :)
The walk to the apartment is hilly, with ups, downs, and lots of stairs, but we've walked steeper paths in Lisbon, so I think it's quite alright if you're mobile. I wouldn't recommend staying in Alfama for anyone who has trouble walking a lot! To go down to the next metro station and the river, it took us 5 min. It took 10-15 min to get to the Praça do Comércio and roughly 20 min to Bairro Alto + Chiado.
We stayed in the beginning of June, in the middle of the santos populares "festival" - so starting from the afternoon until at least midnight, BBQ, music, and conversation can be heard - it was a wonderful, very local-feeling experience (as was the whole stay in Alfama), but just FYI in case you come during this time and are a sensitive sleeper :)
Overall, I can only recommend staying in this neighbourhood and apartment. You really get to experience the warm friendliness of the neighbours, get to explore the streets in the quiet of the morning, and enjoy a wonderful view down to the river.