I stayed at Coskun's place for just under a week. All in all, a fantastic place to stay, I would highly recommend it to anyone!
Location - perfectly located next to Galata Tower near lots of bars, restaurants and cafes. It's in a side street so it's also very quiet.
WiFi - The WiFi has moderate connection, good enough for two people to be on calls.
Safety - The building is very secure and has security cameras in the stairwells and outside. The building looks like it's owned by Coskun exclusively for airbnb and feels very safe. The area itself is very safe and touristy. My gf felt comfortable walking around at all hours.
Kitchen and amenities - Coskun has thought of everything, great kitchen appliances an iron and ironing board along with a hair dryer. The shower is also fantastic with great hot water and water pressure. Further to this there is soap, dish liquid and laundry detergent.
Work from home - there is plenty of desk space and chairs for two people to work from comfortably. There is construction across the road at the moment which starts up at 9am and finishes by 5pm, the noise isn't terrible but can be sporadic I.e. jackhammering and electric saws. Also, the call to prayer is faint to barely heard at all.
Local recommendations - Guney restaurant, very good well priced restaurant around the corner. Federal Cafe, best coffee we found in Istanbul.