TLDR: clean, comfortable, great location, amazing help from David and his handyman Gus.
Cleanliness and location are always my top priorities and Davids flat delivered. The view of the castle is incredible, and access to the Royal Mile area is perfect - close enough that you feel right there, but not right in it for it to be noisy at night. Top floor flat which has its pros (no noisy neighbors upstairs!) and cons (carrying bags up 3 flights of stairs since there is no lift. This was fine for us but good to be aware!).
In terms of communication, absolutely top notch. My husband needed to buy a kilt jacket so I had the idea to start with messaging David about a month out to get a recommendation since he's local - and he gave us a list of about 3 or 4 places to check out, with estimated walking times and notes on probable price range. Since this was not related to the flat itself, I found this impressive. Then on the day, it turned out the keypad for entry had been playing up, so he had his handyman Gus wait for us to arrive to hand over actual keys instead, and sent messages about this. We had the international plan on my husbands phone not mine, so I was only getting internet access on wi-fi and didn't see the messages to give an ETA, and David and Gus were both so gracious about how long he might need to wait (taking advantage of some free time to watch some sports!). Since they needed to get the keys back, Gus came back the morning we were checking out - at 7.30am since we had an early flight - and helped us carry our bags back downstairs which was really beyond any expectation we could have had. He came back down a while later to take out the rubbish, and our pre-booked taxi had stood us up, Gus immediately pulled out his phone to help us rearrange travel too, and waited with us until something arrived. I've stayed in fancy hotels that haven't had staff like that!
In terms of the flat itself: clean, spacious, nicely laid out, everything there. Even a couple of bottles of scotch with a note to help yourself to a wee dram. The only negative I had was that I couldn't figure out how to get the shower hot, but it was warm enough and I'm sure there was a trick to it that I'd missed in the communications and just didn't have time to look for. But overall, a very positive experience and I'd absolutely stay here again.