The apartment is outstanding. You have your own private balcony on the second floor which overlooks Fira. It was newly renovated (we were the first to stay there I believe!), has air conditioning, and is the perfect place for a couple or small family. It's close enough where you are a 2-3 minute walk into town yet serene and quiet. We went for our honeymoon and enjoyed this island and apartment more than any others.
There is a pool which guests can use and only a few apartments have access to. The owners are the kindest people you can imagine. The couple does not speak much English though they always greeted us with a smile.
Katerina was incredible with helping us with our stay. She gave us the ins and outs of Santorini for our ATV tour and answered any questions we had for things to do in town.
I highly recommend taking the bus from the port if you arrive by ferry. The cost is only 2 euro per person and I think we only had one stop before arriving in Fira (5-6 minute walk to the flat). The Fira bus stop also posts the ferry return trips which align with when the ferries are leaving so do not worry as time tables do not exist online.
Fira is the better town to stay in than Ia (Oia). It's nice to go to Oia for the day though we much preferred the less hustle and bustle that Fira offered. Oia seems to be picture overload because this is the town with the blue tops on the houses. Fira has just as good of shops with less madness. Best restaurant on Santorini for food with a phenomenal view was 218 Restaurant (Oia). Best restaurant to watch the sunset was the Vine restaurant (Fira). Stop by at lunchtime the day of to make reservations for dinner and let them know you want to sit on the edge of the balcony facing the water. 218 even let us choose our table. Check the time of the sunset and aim to sit 30-45 min ahead of that. The sunset lasts for some time and has all different varieties of color even after the sun goes down.
I would stay here again in a heartbeat.