We spent 2 weeks in Bera's apartment in Kartal and really enjoyed our stay. Apartment is clean and spacious enough for two people with remote work, it has all necessary appliances and is located in a quiet place. The house also has gym and 2 swimming pools (indoor and outdoor) which we didn't actually use but found them very attractive and beneficial.
Special thanks to the host - Bera is really nice, friendly and helpful person, he helped to look around and supported us a lot - either with advice or with some things we needed. I would definitely recommend this place for a short stay in Istanbul and give 5 starts to the host