The apartment is spacious and suited us very well. We were two couples and a single, so it was perfect with two large bedrooms and one small one. The living room/kitchen was nice to hang out in together. However, do not plan to cook any advanced meals, since there were not that many utensils (no knives or scissors, for example). We only used it for breakfasts, though, so it worked fine for us.
The only downside is that the apartment is by a large road with some heavy traffic, and there were a lot of noise in one of the larger bedrooms. (The other two rooms are on the back of the house and were very quiet). Bring earplugs if you are easily disturbed. However, this is compensated by the ideal location - it just takes a couple of minutes to walk to King's Cross and there are plenty of restaurants and shops in the area.
All in all, we really enjoyed our stay in Iwona's apartment and recommend it!