The flat is in an amazing location (just down the street from the Grass Market) with plenty of food options nearby. Gavin was very responsive and helpful. The flat was clean and an appropriate size for my, my Mom and brother. The flat is very near the the castle (which offers AMAZING views) but also means you are very near the Military Tattoo performance which includes loud fireworks and noises until about 10:30-11 pm at night. This wasn't a problem for us since we were still up but could be an issue for anyone wanting to turn in for an earlier night.
I would highly recommend staying here! It was a fun trip to Edinburgh for the Fringe Festival