Me and my girlfriend spent 3 nights at Keon's apartment and we instantly fell in love with the place. The interior Is modern and minimalistic and everything was perfectly clean.
The area the apartment is located in, is quiet, but the city center isn't far away at all. Whether by bus or by bike it only took us approximately 20 min to reach the center.
Koen himself is very pleasant to deal with. The communication was always friendly and polite. He wrote us several pages of recommendations for our trip to Amsterdam, which was really awesome.
I can recommend Koen and his apartment in Amsterdam to everyone.