Our family of four really enjoyed the location of this nice flat for 3 nights during the Christmas holidays. The hosts were very helpful with communications, and check-in and check-out were very smooth.
The only thing I really think guests need to be aware of is that there is a nightclub next door, and the noise of the bass music coming through from about 11 pm - 3 or 4 am might disturb some people (two of us were not too disturbed, but the others had a pretty hard time sleeping). In fact I'm surprised that no one mentioned has mentioned this in earlier reviews, so I feel it should be mentioned - but perhaps it's not a problem for most. Additionally, the flat could benefit from a microwave, unless there is a technical reason prohibiting this.
In any case, you can't beat the amazing central location - walk to nearly everything in Athens, and it feels very safe. The flat has a nice, clean modern feel yet also style and charm.
Also note from the photos that the bedrooms have sliding doors that are an old-style feel of wood with textured glass panels - light and noise travel pretty freely between rooms, so the layout is probably best suited to a close family vs. separate couples.