Up front, shout out to Benan for being an A+ host/liaison. He was a veritable font of information, and always responded quickly to my inquiries. He's a great asset to the rental team.
I was very happy with my stay in the apartment -- I'm giving it a solid thumbs-up. The kitchen, with excellent appliances (fridge/freezer, induction cooktop, dishwasher, kettle, Nespresso) and ample storage was far above the norm. The bathroom, with roomy shower, first-rate toilet, and ample storage, was also excellent. I'm an admitted germaphobe, and I was very impressed with the cleanliness of the kitchen and bathroom, which are usually the prime offenders. Bedroom and living room were sufficiently roomy and nicely kitted out, and I loved having a workdesk in front of the full-height windows.
As many have mentioned, the neighborhood is great. Sufficiently artsy/boho without being gentrified. This is a neighborhood where "real" people live and work. Excellent restaurants and bodegas, too. If you learn a few words of Turkish, throw in a couple idioms, you'll find that folks will be even friendlier than usual (and I have found Turks to be extremely hospitable as a rule; friendly, outgoing, and inclusive in general).
One caveat: unless you are spry, this can be a difficult area to navigate. There are limited sidewalks; the streets are very unevenly cobblestoned, very narrow, and very hilly. It's a relatively long walk to public transport.
And perhaps most important of all, you are kidding yourself if you think you can summon a cab via Trafi/Bitaksi/Uber/etc. and head out. I once waited 3 hours for a taxi pick-up. Literally, 3 hours and sixteen minutes. And that was while I was fishing for a driver on three different apps at the same time. In fairness, the taxi situation in Istanbul is just dire, period. The number of taxis within city limits is severely regulated. Taxi drivers have a hard row to hoe in Istanbul. Tip well!
In summary, I wholehearted recommend 27 Cukurcuma Cd. It was a great AirBnB experience. I enjoyed my time in Cihangir and can't wait to return.