The best thing, i had free sim card for outside internet and free istanbulcard for public transportation.
As you can read from all excellent comments here KUBİ is the best in Istanbul. I stay in kubi's house for 1 month. there is no any security issue, it was full house, very spacious and fully furnished and all stuff I need during my stay. its very homey just like turkish flats commonly. Kubi is very great house as long i have been using airbnb so far. very fast respond and ready to help you anytime when you need it. also good location, there are so many shop nearby, restaurant or cafe, also easy for transportation. you can use metro, bus to anywhere.
You can ask all your questions and he is ready to answer all the time.
House is very big, kitchen is full, 4 rooms, a lot of beds. Highly recommend.