We've had probably dozens of posts over the past few years about this. It is a converted car-carrying ferry from the North Sea. Some say the 'free' cruises require a condo sales pitch attendance, others say that isn't so. But we've also heard about the extra fees not included in the 'free' part stacking up.
Personally I would never bother with them. I am jaded though, since we've had to ban several 'members' who posted here gushing about this outfit which we determined were actually employees of that cruise line (or their family and friends) trying to drum up business and get free advertising.