We stayed at Olga's place for 3 nights. The check-in instructions were quite clear, and we were able to self check-in at 10PM without any major problems. It took a bit to get used to how the keys operate, but that was just temporary.
The apartment is great and spacious - plenty of room. It contains two bedrooms - we only used one (there are air conditioners in each room including the living room). The balcony is a bit narrow and has the view of the mountains while the Acropolis is visible from the second bedroom. The location is spot-on, just 10 min walk from Acropolis and the center.
We really enjoyed our stay and highly recommend this place anyone who's looking for an affordable family-friendly place near the center.