I imagine it might be quite dangerous to transfer people from one ship to the other in heavy seas, and in the article they were talking about seas of 30 feet.

That's what they wanted to do initially but since everyone wanted to be on the flipped ship when it was flipped they refitted it to house people. At that point you may as well find a way cram them in when it's horizontal rather than incur the cost of bringing them out and back on a separate ship.

There's accommodation for 16 people. I imagine that means something like 4 or 5 showers/toilets/sinks.

Probably more sinks, it would be interesting to see the actual numbers of duplicated fixtures. I didn't find anything with a brief search.

That means you need an additional ship when towing it into position, and more time is wasted transitioning people to and fro. Here everybody boards in port and they can do on-board setup during towing.