Marco's place is located very centrally in Mouraria and it is easy to reach by metro (the Martin Moniz station is at like 4 minutes walking).
The place is small but has everything you need, we especially liked the duplex character with the bed upstairs which made it super cosy :-) The staircase is really steep which makes it a little hard to get the luggage up, but definitely not impossible. I can understand the comments about the cold during the winter months (which is very much a general problem in Portugal and Spain during winter as central heating is very untypical), but we did not actually think it was so bad as there are two heaters that turn the room warm in a matter of 5 minutes, and lots of extra blankets so we did not freeze at all.
Marco is great at communicating from start to end, we couldn't have asked for better instructions e.g. on the self check-in. Also, there was an extensive booklet with suggestions laid out on the table for us to discover.
Very pleasant stay, highly recommended :-)