I stayed about three months in the apartment, to my satisfaction.
Unique provides a nice welcome package with some basic amenities (soap, olive oil, cleaning products, even a tablet for a dishwasher even though there is none ;) and their responses were good and fast enough for me (usually during business hours, so sometimes the next day).
The apartment is decent, and although the neighborhood felt a bit shabby in the beginning, it is located really nicely, with close proximity to a lot of the major sightseeing places and basic amenities like a supermarket. Other reviews mention the bars across the street and while they can indeed be loud occasionally, I had no issues sleeping in the apartment, even though I had the bedroom on that side of the street.