My girlfriend and I stayed at Ergun's place for a week, and found it to be the perfect base for exploring Istanbul. It is well connected in terms of access from Sabiha Gökçen airport (no idea about Atatürk airport) and easily visiting the guidebook sites south of the Golden Horn.
Communication was easy and quick, and the key handover very straightforward.
The flat provided with all we needed for a comfortable stay. Just two things light sleepers should note: firstly, one frosted window did not have a curtain - no chance anyone could see in, but light did come in in the morning earlier than we might have liked. Secondly, the flat is in a street full of bars, which stay open late and are quite lively. Despite the excellent sound insulation in the flat, I was glad for my ear plugs and eye patch.
We found ourselves eating out, but bottled water etc. was very easy to find in the small grocers shops close to the flat. If we'd been a bit more organised/disciplined we could have made better use of the flat's cooking facilities.