I think it is utterly different to the c5. As different as it is possible to be, tbh. 2 wheels at front, fully enclosed, much, much bigger, etc.
Road legal is about being legal. There is a bbc vid with one in use, and the voice over indicates that sinclair the younger thinks of these things as e-bikes and their being used on cycle networks.
If they were used on road networks, I think they have a place, as a kind of velo-moped device.
The cheaper model at £3000 with a 250W motor seems competitive with other velomobiles.