There's a lot of positive reviews on this place (rightfully so) so I'll just focus on the couple negative things I've found.
First and foremost is the bathroom. It's tiny, feels old and the toilet really isn't good. It's all clean but what I mean is that the toilet feels cheap and not easy to use (flush wouldn't work sometimes unless we took off the cover), the sink is right in front of you as you're sitting on the toilet which makes you feel very cramped, and the shower is extremely tiny especially if you're not a small person (we're normal fit people and we still felt it was too small for us). The big water heater is also hanging there which makes it feel even more cramped.
Second is that you're gonna expect a lot of walking up/downhills due to the location, so if you're not taking taxis then I hope you have good stamina and leg strength if you plan on going to Taksim metro often.
That's pretty much it. The rest was really nice. Murat and Alper are very friendly and helpful, comfy bed and sofa, working TV (although not a smart one), air conditioning is good and it's a pretty quiet area. There's a Dominos pizza almost directly in front of the place, a couple markets, some other places to eat and you walk down the street for about 3 mins and you find yourself at the Bosphorous, with a Tramvay and a bus stop that goes to many places. From there you can walk for about 5 mins and you get to the Kabataş ferry station where you can go to the Asian side and also take the lovely Bosphorous tour by ship. Taksim metro and Taksim square are also very close although you'd have to walk uphill to get to them. Taxis got to the place pretty easily, just show them the location on Google maps.
If you don't mind this small bathroom and walking up/downhills (or you're planning to take taxis anyway) then I definitely recommend this place. Hard to find better than this for the price.
Thank you Murat and Alper for having us, it was a pleasure and we really enjoyed our stay.