Based on previous reviews I guess we arrived with high expectations, and to our surprise it turned out to be even nicer than what we were hoping for.
Yes, you will have to carry up your luggage up 4 floors when you arrive (and down again when you leave, plus all the stuff you end up buying), but the apartment itself and the location more than make up for it.
Check-in and check-out went smoothly. We didn't have a chance to meet Diana, but her colleague Jorge met us at arrival and gave us lots of useful tips about what to do and where to go. He also was always available to answer any questions we had and was very friendly.
We highly recommend staying at this apartment and will do so ourselves if we travel to Lisbon again.