I went through the thread from Chris` link and one person mentions that he was quoted £1400 for a single radiator. That post was dated Feb 2012.
I suspect what this company has done is think carefully about design, to make these blocks of firebricks look more sexy, plus engineering work to make the heating control more intelligent, plus using foreplay that packs more heat in per cubic metre of fireclay.
None of this impresses me if if drives the price up to that extent. Electric storage rads are the simplest of products, convert 100% of the electricity they consume into heat, and the big issue then is keeping that stored night heat inside the device long enough to allow it out at a controlled rate to warm the room. The company doesn't say much about the insulating layers around the fireclay.
Like Chris, I'm sceptical about companies that sell only via their own salesmen in your home. They are likely to sell the features hard, make claims about benefits it is hard to verify, and use these two to justify a higher price.