I doubt if you would have space in your panniers to carry that great thick guide book!
I had a similar card issued through the CTC a few years ago. It never did earn me the promised discoounts, but was handy in that the site owners just copied your details off the card when you arrived on site, so no more filling in of foreign language forms. Also some camp sites like to retain your passport, but most were happy to hold on to the card instead, which I preferred.
My card also offered some sort of insurance which this card does not appear to do.
A little more research required before parting with your money perhaps.