First off, communication before, during and after our stay was great (through WhatsApp). We were personally checked in by Chiko's cousin who showed us everything in the place - we even met him once at the tea place next door, and he invited us to join ;-)
It really is within short walking distance of Galata Tower and the cousin helped us with the luggage.
The place was pictured in the listing, and had been cleaned just before our arrival. The bathroom was simple but also clean; and the fridge was pre-stocked with a bottle of water. The kitchen(ette) has the basic equipment - as pictured - and is enough to whip up a simple meal. (Air-conditioning was out of order when we were there, which can happen. Chiko provided fans for cooling, and assured us that by now a new and improved unit has been installed for future guests.)
The location was really great. This was our first time to Istanbul, and the Galata area seemed much more laid back than the Sultanahmet/Eminönü side where all the "must see" spots are. You'll find food and drink places nearby and you can be at the Galata bridge within 10 minutes of walking. A collection of guide books was in the flat, in case you forget yours.
The best part was the rooftop terrace, which was great to enjoy the sunset and offered an amazing view on the Golden Horn and most of historic Istanbul. Just grab a few beer and snacks from the supermarket around the corner and enjoy.
You can reach Galata tower easily by taxi or public transport - given the current state of the Turkish Lira, getting a taxi to/from the airport is quite affordable compared to other major cities.
We stayed at the apartment as a couple, for which it was perfect, and you'll probably with 1 or two smaller children on the couch. (Staying with 4 adults is also possible, but I guess you'll have some "hostel dorm" feeling in that case). Note that this place isn't for you if you are of limited mobility - you must be able to navigate a flight of stairs to get there.