Overall, the stay was very good.
To start with the negative, parking is, well, exactly like you would expect in the middle of a city, which is to say difficult (we had some luck on Sloane St and Dickson St). There are a lot of stairs but they aren't really that bad. It may be user error but we couldn't get much water pressure from the shower.
On to the positive, of which there is a lot. The flat looks amazing. The host is obviously talented with design. There were lots of small details and thoughtfulness that you simply can't get with a hotel that was really cool (for example, there was proper bread and jam to eat and milk and butter in the fridge, as well as tea and coffee). The location is fantastic for walking to Princes St or Leith, and there are a ton of shops and restaurants on Leith Walk within a couple of minutes. Check-in and out were super simple and we could get in contact with the host very quickly if there was an issue.