This is a very cute but tiny apartment! If you are compact and don't mind stepping over each other a bit you'll be absolutely fine. Vasso is a fantastic and responsive host!
In the summer it is probably even better as the balcony space is huge - unfortunately when we were in Athens the weather was awful so we couldn't capitalise on this awesome space.
The fridge was handy as we could buy food at the supermarket (7mins walk away) and make breakfast and lunch. The bed was comfortable and a good size for two.
The bathroom is a bit cramped but this isn't really a big deal.
The area is very cool with plenty to do in the evenings, it's not too loud but if you're a light sleeper bring earplugs.
There are 4 flights of stairs to climb to get to the apartment with no lift, so if you have trouble with stairs/lifting things you should be aware of this. Good fitness though.