We had a short stay at Mehmet’s and had a good experience:
-Location: excellent. Less than 2 minutes walk from Taksim square. You can expect noise from nearby discos /pubs until midnight or so but it wasn’t an issue for us to sleep well after a day-long walking.
-Apartment: basic furniture but with very comfy beds! The apartment was clean and everything functional. The apartment is in the second floor with no elevator.
Also please note that the water heater is installed inside the second room (as for most of the old apartments in Istanbul).
-Host: Mehmet was responsive and precise about everything. We had a simple self check-in and check-out.