Barbaros was a wonderful host, frequently inviting me to freshly made tea/coffee downstairs, giving me tips for navigating the city, and even getting on the phone to deal with a taxi driver trying to rip me off (note to others: the toll charge for the Avrasya tunnel from the airport is just 23TL - don’t let a taxi driver try and charge you 70 “to cover his return”!).
The place is really very nice and spacious, pretty much exactly as it looks in the photos. The location is great, within walking distance of all the major attractions (although fair warning - Istanbul is hilly!). The WiFi is ok - fine for looking up things but too slow to watch videos etc. You can pick up a SIM card if that's an issue - I paid approximately £20 for 8gb at the airport, probably would have been half that in the centre. It can get noisy from the nearby restaurants, but if you’re going to bed before midnight in Istanbul then you’re really doing it wrong!
One thing I would say - if you’re a non-smoker who has a very sensitive nose, you might be best avoiding this place. Smoking is more widespread in Turkey than in the UK, and the apartment is saturated with the smell, both in the furniture and coming from other apartments. While staying there I somewhat got used to it, but after leaving I had to air out my suitcase and wash all the clothes I took with me - even the ones that didn't leave the apartment - to get rid of the strong smell I didn’t realize they had absorbed. No long lasting damage done, but it’s just something to be aware of.