I stayed at Dimitrios' place for a month, splitting my time between a holiday and work. I think this gave me a well-rounded understanding of staying in the apartment. Overall, I think this apartment shines for short to mid-term stays. Its location (just steps away from the Petralona metro station (green line) is unrivalled. There is also a bus stop just down the street. If you're in attends to explore, you couldn't have an easier time. If it isn't too hot, you can definitely walk to various tourist attractions too.
The apartment itself is very spacious and has all the modern facilities you'd expect. There are plenty of shops, bakeries, cafes and restaurants in the vicinity. Petralona itself is pretty quiet. For my working time in the apartment the WIFI was serviceable and didn't give me any issues. Having said that, Dimitrios is in the process of getting faster WIFI which would definitely elevate the experience.
Dimitrios was available for any questions and fast to reply. When I reported something breaking in the apartment he came over the next day to try and fix it.
Overall, I'd recommend this apartment most for people that come to Athens for holiday. You'll have a great stay and convenient base to explore Athens from.