I stayed with a colleague in Susan's comfy and spacious apartment on the Southside of Edinburgh for the Festival. As Susan wasn't available when we arrived, arrangements were made for us to collect the keys to the apartment from the Ichiban restaurant next door. We drove, unloaded and parked up on Regulas road which is the nearest free parking. It's about 10 minutes away on foot.
The apartment is at the top of the block and is perfectly adequate, particularly the room itself which is clean and spacious. There's tea and coffee-making facilities and plenty of maps and ideas for your trip. There is a shared bathroom which again is perfectly adequate, but please communicate as this currently isn't lockable. Breakfast isn't included but there is a lovely tapas place on the corner and two or three other breakfast places are nearby. We were perfectly happy to make our own arrangements anyway.
Susan wasn't around for most of our stay as she was going on holiday. She was pleasant and helpful, as was her niece Isla who took over hosting duties. We could have used the living room in our 'down time' but chose to chill out in our big bedroom.
We stayed for four nights and explored much of Edinburgh on foot. It is very easy to get to the Summerhall, Gilded Balloon, Udderbelly and Pleasance festival venues in particular. If you like to run or walk, it is also a great location for a trot around Arthur's seat. It is a lovely walk through Holyrood Park to get to the Parliament, Palace and Royal Mile. The area is extremely well serviced by buses which we used to explore further afield places like the Royal Yacht Britannia at Ocean Terminal. There are many decent pubs and restaurants nearby too.
I can recommend Susan's apartment for your consideration. It was only my second Air B & B experience and everything worked out well.