We never stayed on a houseboat and loved it. The deck is amazing to sit on when the weather is nice, everything was clean. The second bed is in the living room and a bit outdated, would recommend it for three people, four is possible but cozy.
The location is perfect as it is close to all places you want to see in Rotterdam, everything is walkable. We never met the host but we got super quick and nice replies. Can definetly recommend it! :)