Just looking at another website....
http://www.london-se1.co.uk/news/view/7368
The seats look very hard. I don't fancy riding all the way from Peterborough to Brighton on these. Also there are no dividers between carriages. I wonder if this is the case throughout the whole 12 cars. The whole thing looks crude like an underground train.
If this is the case it's a major step down from the 377s currently providing the service.