I would absolutely recommend staying at Martin's flat! The flat itself is very nice, stylish, and was sparkling clean.
The location was excellent, just below the castle in the grassmarket area, full of shops, pubs, and cafes. It was also very close to the Royal mile and just a 10-15 min (very scenic) walk to the new town.
Communication with Martin was great, he was very responsive and made sure all our arrangements were taken care of. He also welcomed us with a quick intro to the city and major sights, along with some recommendations. He also left the flat well stocked with bread, eggs, milk, tea/coffee, so we already had everything we needed for breakfast! He really went above and beyond what we expected. We had a wonderful time and we're only regretting not staying longer!