We would highly recommend staying at Dev's apartment. Great spot, easy access to public transport, very safe. Dev was very helpful — her guide to Istanbul (restaurants, galleries, sites) was brilliant. We spent a few nights in the Old city before moving to Devs apartment, but in hindsight we should based ourself at Dev's the whole time as it offered access to a far more authentic Istanbul. Its also very easy to access the main tourist sites in the Old city from here via public transport.