Location wise: Perfect.
We've never used a 3rd party mgmt with AirBnB before, so that was a new experience for us. Turns out we do like and appreciate the little touches left by an owner, so if that is important to you, then take it into account when you book.
When we arrived at the flat, there was someone else parked in the space (which later we found out the bollard didn't have a proper lock so other people could access the spot), but when we contacted Altido, they responded quickly and advised us to find parking and we'd be reimbursed for it. After a 4 hour car journey (with kids who were over tired), this was slightly annoying, but we appreciated the gesture. Luckily we were able to move the car once the space became available again.
The flat itself was functional, but basic. Mattresses were comfortable, and because of the location we were close by to everything, which was really nice!
Another thing to be aware of, especially if you're staying with children: because of the central location, there are several alley ways we ventured down near the flat. We did run into a fair share of drug users, etc - which we expected due to the festival. I suspect it may be like that year round, so another thing to take into account when you book.
Overall, we had a good experience here, would book again. Altido also was responsive when we asked questions. We had a lovely trip to Edinburgh and can't wait to return.