4 of us stayed at Vefa's place for two weeks. Overall a positive and comfortable stay, and it felt like home.
Positives: good location with nice and quirky cafes and shops right beside it. The flat was given to us clean and tidy, and the bedsheets/towels seemed to be professionally cleaned. Vefa has been very responsive, usually within a couple of minutes; and when we needed extra bedsheets and towel, he quickly provided those to us.
The slight downsides were: at nights it can get noisy, especially in the weekend (ear plugs while sleeping easily solved the problem for those sensitive). The temperature of the water in the shower was not staying stable, and it was often getting cold or too hot.
If we go to Istanbul another time, we might not stay in the Taksim area, but we would happily stay in one of Vefa's places if available.