From what I can gather, you basically stab the attacking predator, then press the button behind the top of the guard to release the CO2 gas, which is contained in a standard disposable cartridge. Here's a cutaway view of the knife:
Seems like it might be useful in an underwater situation against, say, a shark (although a bang stick seems like a better option). Against a human attacker, however, the attacker might have something to say about letting you just fill them up with gas -- "excuse me a moment while I activate the inflation option on my knife"? At the very least such a strike would require some good coordination to avoid discharging the CO2 prematurely, although I couldn't determine from the product's website whether the discharge can be controlled into multiple bursts, or if you only get one big burst of CO2.