Celal place has a very good location - just 5 min walk from Sultanahmet with Blue Mosque and Ayasofia. The neighborhood is full of different kinds of shops, street food, groceries and supermarkets.
The apart itself is good for stay. I visited Istanbul together with my kids in January and I was afraid that we may have troubles with heating or hot water, but everything was excellent. The heating was so intensive, so we had to reduce it a bit.
Also, what I found important, is that the bedrooms are located on the quite side of the building and we were not disturb by sounds of street traffic or anything else.
Celal and Ismail are very hospital and gave us many useful advices.
I would rate this place as the best in terms of price/quality.