I stayed at Günay's place for 1 month. There was a lot that I liked but a lot that was lacking.
Overview: the place is a 4+1 apartment which was converted into a 5 bedroom apartment without living room. There are 1.5 Bathrooms. The place is managed by Mr. Asrin, whom is Günay's employee.
Let's start with the positives first:
1) Mr. Asrin - he is very hospitable and tries as best he can (and he is very constrained) to provide the best situation possible. Additionally, he is very communicative and responsive.
2) The bed - it is very comfortable. If it is not summer, you will sleep very well here.
Now the negatives:
1) The toilet: the main toilet had a problem with flushing - often it couldn't flush and it needed someone to attend to it to fix it daily making it unaccessible during this time.
2) the bathroom smell - there is a strong sewage smell that comes from both bathrooms - when informed about this the problem was ignored
3) the electricity will cut out on you - this happened roughly 5 of the 28 days I was there
4) the wifi was spotty
5) There was hardly ever toilet paper present and often soap is running out or out. They have a bidet, so much toilet paper isn't needed - but some is. I was informed that they don't provide these for long term residents - their airbnb page says they do. Also detergent for washing was not provided.
6) The room has very little air ventilation and will be significantly hotter inside than it will be outside.
7) the kitchen was okay at best
With all of that said, this is the final and most important point of all:
8) Stinginess - it is clear that Günay is attempting to limit all of his variable costs in order to maximize the return on his investment. This means that:
1) When asking for more pillows, I only was given one
2) the closet door key is jagged (it will cut you) and you can either get cut, or leave your
closet open like you live on a barn.
3) You will not be provided a fan during the summer months (this request was denied)
4) Your bathroom will smell and they will not attempt to resolve this (or address the
concerns)

TLDR:
If you are staying in Kadiköy short term, if the weather is under 20 and you're planning on spending minimal time in the room, this is a decent place to stay. However, from a value perspective, it will make sense to stay elsewhere.