Yeah I used it two years ago with my lad on our Norway trip. Colour line is the company we used and our boat was Color Majic. More like a cruise liner than a ferry really. I think it was about €1000 for two of us, two bikes in an outside cabin including meals. It’s around 20 hours for the crossing. I would other with the meals if you are not a large party as there are plenty of restaurants to choose from on board.
We met up in Hamburg as i didn’t want to be racing the clock getting from Rotterdam to Kiel in one day. It’s in all likelihood possible but a hold up can be very stressful and perhaps expensive if one misses their boat.