We enjoyed our stay at Elvin's apartment. The location is pretty good: close to Beyazit tram stop, Grand Bazaar, the Blue Mosque, etc., many shops and street food nearby. The apartment has modern design and is well-equipped.
Only a brief warning - it is better to keep the bedroom door closed for the night as the acoustics in the apartment are not too great and you can pretty much hear everything the neighbours downstairs do in the kitchen and bathroom :)
But all in all - a great stay and recommended!