Normally i would shy away from unknown (or known bad co2) but i took your bait! Often these non-food cartridges have impurities or even oil to keep whatever they're pressuring nice and lubed up. That's why the food ones cost more, they have to take extra steps to make sure they're clean.
Take a look at RavX's website, interestingly they say it's food grade gas... but should give them a call just in case (something's on the metal, etc):
But in general these little co2 cartridges are very expensive per unit of gas and it's much cheaper to go to a welding shop and get a 5lb tank.