Highly recommended. The location is excellent, just around the corner from the beautiful Galata Tower, and very close to public transport links to other attractions/neighbourhoods like the Ayasofya and Topkapı Palace or Beşiktaş. Within a five or ten minute walk there are great restaurants, bars, and the Kiliç Ali Paşa hamam (well worth a trip). The terrace gives you a stunning view of the city that you don't have to pay extra for or share with other tourists.
The hosting was great as well, we were a little lost on our way over, as was our taxi driver, but someone was there to meet us and make sure we were settled in. The flat itself is very comfortable with two double beds and a single, but is probably better suited to people who are planning on spending most of the day enjoying Istanbul (if only sightseeing from the rooftop terrace), rather than lounging around the house.
Fantastic location, fantastic hosts — I'm 100% sure I'll be visiting Istanbul again, and this would be the first place I would try to book.