On the other hand, the thickness is because the whole front slides down to reveal a Bluetooth keyboard. The Bluetooth also allows you to use the case's flash off camera for helping with things like harsh shadows in portraits.
The C.4 is basically the V.4 without the Bluetooth keyboard. You still get lenses and the built-in flash and shutter release, all for the low, low price of £199, or about $319.
A third version, the V.5, is actually more of a full camera, with a 14-megapixel sensor, imaging processor, a 5x zoom lens, and built-in flash. The iPhone will power the camera's functions and, of course, give you access to apps for editing and sharing.