I want to start by saying that the reviews claiming this is in an unsafe location are completely false. It's likely that a lot of the reviewers have not lived in/traveled to many large cities. I am a solo, female traveler with blonde hair and blue eyes (i.e. I stick out like a sore thumb) and not once did I feel unsafe.
There are a few 24-hour establishments on the same block, so there are going to be people around at all hours of the night. That doesn't mean that they're sketchy or threatening (99.9% are not and having 24-hour establishments, especially during COVID, is a blessing). Yes - there are unkempt people around the neighborhood, but unfortunately, with the current state of the world, that's going to be true of any city. Be kind, mind your business, and just keep walking. However, if you're scared of those things, maybe look for a spot elsewhere. I'd say the only thing you need to worry about in the neighborhood is crazy drivers...but that's a problem all over Greece lol. Pedestrians DO NOT have the right of way, and there aren't many crosswalks. Look both ways...several times.
Now - let me dote on this amazing place. What a beautiful, clean, inviting flat. The WiFi is fine, there is a television that has some basic local channels (I was so happy to find the BBC as it isn't widely available in the US) and the ability to hook up to Netflix, and the bed and sofa are great resting places. It's very close to some lovely restaurants, a 3-min walk to the metro (M2), four stops from the Acropolis, and walking distance to the Central Market and all of the amazing spots around it. The washing machine came in clutch, as I packed lightly for a 2-week trip and left with clean clothes!
The ONLY complaint I have is that there was a lack of cleaning supplies. There was a broom outside, but nothing to wipe counters with (except the sponge for dishes). There was a vacuum in the closet, but the power cord was missing, and I had to purchase detergent. I was anxious that I was gonna spill something or break something the entire time. I also did not find any extra blankets, so napping on the couch required me to take the duvet off of the bed. Also no shampoo as noted on the listing (which was fine because I brought my own, but I know a lot of people don't).
All in all, Mema's place is a great spot for any type of traveler. Great value and hope to return again in my next trip to Athens!