We stayed for 5 or so days - we loved this place and we highly recommend it. Location is great- right in new town and close to lots of restaurants and shopping, including grocery stores. It's about 15min walk to old town with the castle and older building and tons of tourists. The place was sparking clean, very modern fittings and well appointed. Sonia and Chris were extremely responsive and check in was very smooth. We did not meet them but they have an amazing insiders guide with lots of restaurant recommendations which were very good. We particularly recommend Baba's - went there the first night by my self and later went back with my wife when she joined. Very nice place (make reservations if after 6:30pm).
What you need to know: 1) The apartment is in the center of town, so there's some noise from the street below, but we felt it was fine and were not very bothered by it. There were also some doves that seem to live near by - they make a lot of coo-ing noises . 2) there's steep stairs to get to the apartment - we thought it added to the charm but some might find it difficult to carry luggage up. 3) The apartment and rooms are good size and it has everything you need - it was spacious for the two of us. I think it would fit 4 fine if you don't mind a bit closer quarters. More than 4 will start to feel tight I think.
Overall, highly recommended - we would definitely come again.