We've spent a month here and had a positive experience. It is a nice small apartment located right at the center of the city 5~10 mins walk to Taksim station, the same to Kabatas ferry and T1 tram.
Everything's in working order and the internet is rather fast and reliable. The only issue is a bit shabby bathroom, but it seems to be rather common in old areas of Istanbul.
There's occasional noise on the weekends from the bar on the roof of the nearby CVK Hotel, but they stop the party by midnight, so it's ok. In general, the place is relatively peaceful, considering the location. The Migros Jet store is just around the corner and bigger Carrefours are not so far away with a good selection of small cafes and restaurants south of Istiklal.
As a bonus - there's a glimpse of Bosphorus from the living room.
The hosting team is very attentive and welcoming, we'll definitely consider their accommodations next time in Istanbul.