I lived in the “Boutique” for three months and want to provide the following mentionable insights.

Beforehand, the appartment is to be recommended especially for short-term stays, couples, and travellers who want to experience the various sights of the vibrant metropolis of Athens.
Location & Security: The central location of the apartment allows to reach a lot of the surrounding neighborhoods on foot, including Monastiraki and Plaka (below the Acropolis), Omonia and Syntagma (the biggest hubs of the city), Exarcheia (the left-anarchist quarter) or Gazi (with a variety of nightclubs and the Technopolis City of Athens). By means of the near metro station, all quarters can be quickly accessed, anyway. Every Wednesday there is a farmer's market in the parallel street of the apartment, where fresh fruits and vegetables can be purchased. While Metaxourgeio (location of the flat) is not the most representative neighborhood in Athens, I do not share the equal level of concerns about night-time danger expressed in other comments. Especially compared to large cities of similar size, I experienced my residence in Athens to be relatively safe. Besides that, the apartment has a door with triple security lock.
Facilities: The flat, very functionally equipped, is in a good condition. Kitchen and utensils mostly fit the expectations of a long-term stay, so that own cooking is possible. For four people, however, the apartment could be confining in the long run. As a student with a lot of desk work, I especially missed a real table. The existing side tables were unfortunately not sufficient as a work surface. In spring, it can be very cold in the apartment, so slippers should be brought along. Due to the floor plan, natural ventilation is not constantly feasible.
Service: Remote communication with the Spaceers commonly worked without constraints in a friendly manner. However, it should also be noted that the landlord is a company and not a host in the traditional AirBnB style. The private company has 24-hour on-call service.
Overall and again, the appartment is to be recommended especially for short-term stays, couples, and travellers who want to experience the various sights of Europe´s second oldest city.