Is this one question, or two separate ones? Should you find yourself in a zombie apocalypse, and you believe that lighting a deck of cards on fire is an appropriate way to defend yourself... then yes. I recommend that you do exactly that.
I would argue that these cards are of more use as a deterrent. It's been proven in approximately zero clinical trials that excessive use of this product creates a slime-like coating (of pure evil) around your brain that makes it difficult for zombies to smell it.
As for flammability, I would recommend strongly against using this product while on fire -- in fact, I think there should be a disclaimer to this effect. Successful use at Burning Man does hint they can be used within the same general proximity as open flame. I believe the actual flammability of the cards themselves is likely somewhere between the two.