The theory I've read is that most appliances are designed to burn propane. Using a higher butane ratio can, in theory, leave behind more unburnt combustibles, which displaces oxygen.
That being said I knew a couple of farmers who refilled and used autogas for years in their homes. They're both DEAD...
...from old age.
Anyway, great price on those bottles Martin. I'd get one if I didn't have so many 9kgs at home. Can your contact source pure argon bottles?