I'm not sure it sounds that great... by relying on a Facebook page instead of going to the trouble of setting up an actual website they haven't created the greatest of impressions.
As a teacher (in Lewisham) I'd say that 15 pupils per class is far from ideal (IME 20 is a good number for social reasons and for learning) and it seems strange that they would use the National Curriculum and levelling but haven't explained why. There's not nearly enough information on their FB page, especially considering how much more is available about Primrose Primary, another Brockley-based free school proposal (albeit one that is no longer active).