This was our first visit to Edinburgh, and should we return soon we'll definitely try to re-book Kate's apartment.
It's large, comfortable and comfy. Everything we needed for cooking was there, so we took advantage of the nearby Tesco Express to stock up on basic supplies. The kettle is fine for tea and instant coffee, but note the breakfast place across the street has excellent take away coffee as well.
Everything in the city's core is within walking distance, including Waverly train station, but I wouldn't recommend dragging any large heavy bags from there (it's only a 2-minute £3 Uber ride away… save your strength!).
Beds are comfortable, we slept well every night. As others have mentioned, you can hear the neighbors TV at night, but it's quiet and muffled and didn't bother us at all.
We didn't have a chance to meet Kate personally, but she was super responsive to our questions and for anything else we needed.
It wasn't festival time during our visit, so it was very quiet. Looking forward to our next visit!