My stay at Grey Matter 2 was amazing. The place is at an excellent location for a tourist, close to restaurants, metro stations, the museum, and all sorts of helpful places right at walking distance. The instructions to check in and out were sent out in advance, which was very convenient because I checked in at night and didn't need to coordinate with someone to be there for me. The room and services were great, very comfortable and clean, and I found the value of the place against the cost to be quite a deal.
I recommend Grey Matter to anyone visiting Athens.