Henri & Mel were excellent hosts. They made sure we felt ok at all times, but also gave us privacy during our stay. It was also convenient to have them around (upstairs), since they'd immediately answer and help us out when we needed.
Although the apartment itself does not have a lock, there're two cameras in the staircase and the main door to make the guests feel safe, and the main gate's locked by them during the night.
The neighborhood is marvelous: beautiful canals around, super quiet (even with an open window!), but also a few mins walk away from the center.
There were also a couple of things in the apartment that were very pleasant and unexpected: equipped fridge with many things for breakfast (free), a robe, mosquito nets, an anti-fog mirror in the bathroom, and a couple of umbrellas!
We will definitely check Huis Roomolen for our next trip to Amsterdam!