In my honest opinion, the best thing about this flat is the location. It is close to a ferry boat stop (without stairs!) and walkable to the airport ferry stop (some stairs but manageable). It is away from the real touristy area and feels "off the beaten track" but walkable to all the main sites. It is also very close to a grocery store and a nice restaurant with reasonable prices.
The flat is really a "half-basement". It has a comfortable queen bed in a separate bedroom, and a double pull out couch in the living room. It was perfect for the kids to sleep on.
I would recommend this apartment for a family of four or a couple but it might be a wee bit snug for two couples looking for their own "space".