Martin's place is worth of every penny. The location near to Grass Market is great, especially to those who likes to explore Scotland through it's drinks and cuisines. The neighborhood is very quiet and the grocery store and bus stops are only couple of minutes away from Martin's apartment. To reach those you need to climb quite steep stairs though and there's no handrail (it isn't a problem but if you're needing to use a cane or other aid for movement, I'd take it into consideration).
Apartment itself is very cozy and it has everything you need. You don't have to worry about breakfast for the first morning, Martin has it all settled (coffee, tea, cheerios, bread, jams etc.) and if you want something else, just let Martin know and he'll get it for you. I loved to listen pigeons love talk during the breakfast... without them you'd feel there's no neighbors at all. :)
I found the apartment a bit chilly on my first night (mind you, I come from country where it gets -30c during the winter time) and I was a bit apprehensive to add the heating up even Martin told me how to - eventually I decided to do so though and I didn't feel cold during the rest of my stay.
Communication with Martin was beyond great - before, during and after my visit. I would highly recommend this place for everyone who doesn't mind to climb to the 2nd floor. I will definitely rent this place again if it's available for my next trip to Edinburgh. Martin, you are superb!