Excellent deal for those who want to travel outside of school holidays. Cabins are extra and vary depending on crossings and travel times. Day crossing cabins are cheaper.
Worth nothing that the 8 days is time in France so you can maximise time in France by booking carefully.
Can't take advantage myself due to having children at school but use Brittany Ferries a couple of times a year and can say that generally they have excellent customer service.
When eating on board all of the restaurants/cafes offer children's meals for £5.50 which includes a drink and a back pack of goodies. These are decent meals for the money.