I stayed at Tereza's for a month, and loved my time there. Check-in was very smooth, no issues. I found the apartment a great size, bigger than it looks, very comfortable sofa and big queen size bed (TV's in both rooms). Kitchen is small, but has everything you would possibly need. Washing maching/hot showers etc - all working well - had no issues. Air Con was really good - no problems here.
The area/location is very central. Kolonaki is upmarket part of Athens and has lots of coffee shops and cute places to eat - they are lit up nicely for outdoor eating in the evening. You are about 15 minutes walk to the centre. I would say its a great location as the area is quiet in terms of traffic but lots going on and you are walking distance from the centre.
I would definitley reccommend Tereza's place for short and/or long stays. Tereza was very helpful/thoughtful too.