We stayed here as a group of five 30yr old couples, for our friends' wedding.
Location - a fantastic spot, right near the Castle and Princes Street Gardens. Took us 15 mins to walk from Waverley station (with a bit of luggage). Taxis and Uber's also very easy to get from outside, including space for them to pull in (might sound daft but was most useful when you're trying to herd 9 sheep out the door). Quite a few eateries and bars nearby, and a Sainsbury's local right across the road (or a good and cheap cafe next door if - like us - you weren't up to cooking breakfast). Sited above a pub but because the flat is 3 stories up, we didn't hear any noise.
Inside - great layout. 5 double rooms with bags of storage space and room to breathe. Only one shower but even with our large group we coped fine - never ran out of hot water. Very clean (my other half is a stickler for this and she was impressed) and clearly very well maintained by Yvonne. Not a huge amount of living space - having all 10 sat down in one go would be a squeeze, but we never had that situation, and why would you want to a city centre flat to stay indoors?!
Host - great communication from Yvonne. Gave us loads of info beforehand and was very flexible - one of our sheep was flying in separately so needed to check in early. Yvonne was very helpful and no doubt busted a shift to turn the flat round quickly from the previous guests.
Overall - great value particularly given the location. Would definitely stay here again as a large group and would recommend to others wanting something similar.