Overall verdict:
I don't think we could have found better value for money, the flat was just what we needed for a great Fringe festival long weekend. I'd have no hesitation in recommending this flat or Lorraine as a host.

Further detail...
The good:
Lorraine was very friendly & welcoming which set a good tone for the stay. She provided maps/booklets about the fringe, which was our main reason for visiting Edinburgh. She also left basics in the kitchen even though there is a little supermarket across the road.
The location is great, very convenient for the festival venues, we always walked.
Plenty of cafes, supermarket, restaurants and bars nearby.
Flat is actually quite large by European inner city standards, especially the living room. A pleasant surprise given the price.
The shower water temperature and pressure were great.
Clean and comfortable.

The not as good:
Honestly, not much I can think of. One of the bedrooms is smallish, but we found it perfectly adequate for 2 adults and our bags.
The beds aren't large, but unless you and/or your partner are to the extent you need a queen/kingsize, they're also adequate for 2 adults.