My mom and I really enjoyed our stay at this apartment. There were some minor inconveniences, but other than that it was very clean, the bed was super comfy, the kitchen is well-equipped so you can cook whatever you wish. The location is great too, it's well-connected and there are many different means of transport that could get you anywhere you like.
Although there are two things I'd like to point out as areas of improvement:
1) Wi-fi. It's pretty unstable and disconnects a few times a day, and it was crucial for me as I had to get some work done during my stay, but if you're only in Istanbul for vacation, that should be fine;
2) Check-in / communication about mandatory processes. The host texted me 2 hours before check-in that if we don't submit our passport pictures within the next hour, our reservation would be cancelled without a refund. The fact that you have to submit your passport info is indicated in the listing, however, it is not easy to find and I would've liked to receive a reminder at least 1-2 days before our stay + it doesn't say on the listing that your stay will be cancelled and you won't get a refund if you fail to do this. This was a very stressful situation for me so be careful with that.
Otherwise I would recommend staying at this apartment!