We've stayed two days with my wife on Mike's place. It was perfect for our needs - clean and quite.
Location is great - exactly on the city centre. You are very close to most of the popular places. There are some nice coffees just nearby for quite breakfast.
The apartment can fit 4 people but they will share common place.
If you come with a car normally it is preferable to find a parking spot in the centre of Thessaloniki - there are view close the location.
I would recommend Mike's place for newcomers in the city as well as to regular visitors.