I booked Dirk's apartments twice now. Both were fantastic. We had everything we needed. Nice clean kitchen full of snacks, very clean and stylish bathroom and large rooms. Well last time we were there we were 6, so of course rooms weren't enough :) But we didn't really care as we only used the house for sleeping :)
As a personal note, I find Dirk extremely professional and friendly. We had long chats with him during my stay and enjoyed his company.
I will definitely give him a call next time I visit Amsterdam.