Staying at Osman's apartment was great - the place was clean and tidy and the view was to die for.
It is located in a hip/arty neighbourhood (Beyoglu) which adds to the appeal, although the streets are windy, often confusing and hilly. Google Maps saved me from going in the wrong direction a few times. Having excessive amounts of luggage can also be a problem due to the steepness of the streets and the many flights of stairs to the apartment. It is not suitable for people with reduced mobility. Getting around town was easier than I thought - the tram is an easy 5ish minute walk and will take you to many points of interest (and you can use the public transport card for all types of transport - ferries, trains, buses, funicular).
Osman responded quickly to all of my messages and even turned up at 4:30 am at check out to assist with the airport transfer he'd organised for me. Overall, I felt well looked after and safe.