Omer's place is very centrally located for all the tourist attractions in istanbul. Also very close to sishane m2 metro line. I have no bad things to say about the place but tourists should keep few things in mind;
-Place is located in an area where all the streets are very narrow(there were no cars in 1500's) so i would highly recommend NOT to take taxi.
-if you are light sleeper, call for prayer from nearby mosque might disturb you(it didnt disturb me though), although its a turkey thing.
Omer is very helpful and answers promptly to any question you might have. Apartment is quite big considering istanbul standards and price is quite good. There is aircon in living room AND bedroom. Kitchen is fully stocked with whatever you might need including coffee,tea,salt,utensils etc.
also you will see an easy way to order groceries/restaurant etc posted on the door when you enter the apartment. Small but an important detail.
Additionally, if you have heavy luggage, i would highly suggest you to get a flat that is on first or second floor since there's no elevator and apartments in istanbul has really narrow stairs. I had no issues though.
overall place is quite good and you wont be disappointed as a tourist.