What a location. My advice.. take the offer of an airport pickup. The 30euros may seem a bit steep, but when you realise the route you would have to take form the nearest train station to get to the apartment and the hills you would have to heave yourself up, along with your luggage, it'll seem a bargain! Plus, you given a whistle stop tour of Lisbon by Pedro on the way.
You are situated only short stroll away from Castelo which and location wise it is fantastic as it means you are looking down on the rest of Lisbon. Be sure to bring your walking shoes or a very comfortable pair of trainers because as a base this is a great spot to explore Lisbon from but you will cover some serious miles/km.
The apartment is just as described, compact with a small balcony. It has all the amenities needed and has wifi, although it isn't the best if you like uploading pictures, blogs etc from the comfort of your apartment. But in no way should that detract from this flat.
The area is safe and feels vey homely and you have a Mirador all of 5 mins away from which you can see across Lisbon and beyond! You will read in other posts people comment on the stairs leading up to the flat, they are steep, but this is only really an issue if you have trouble getting up stairs. Should you be considering where to stay... Make it Castelo and make it with Sarah and Pedro.