We stayed at Mathias apartment for 6 nights and it was great! The room is big enough for two persons, clean, with new furniture and a lot of light all day. The big advantage of the room/apartment is the location which is really central, near Rossio, so you can walk by foot everywhere. Moreover, the neighborhood is authentic and not too touristy, which we really liked.
To finish, Mathias was a nice host and answered all questions we had. We really enjoyed our stay in Lisbon!