More relevant information from the link:

*NOTE:The cinnamon powder that you get in the super markets could very well be sawdust that has been coloured and artificially flavored. I think it is better to get the bark and powder it yourself. Most spices are irradiated. This is supposedly done to eradicate bacteria, but spices are generally excellent bactericides so the irradiation is merely a way of destroying the precious properties of spices. Non-irradiated spices are available from most high-end health foods stores like the one below. Cinnamon can be confused for cassia and in fact many powdered forms use cassia ( [link to en.wikipedia.org] It is also known as “bastard cinnamon”. True cinnamon is also known as "ceylon" cinnamon. There are other variants such as Indonesian and Vietnamese so avoid anything that is from these countries. Specifically ask for Ceylon Cinnamon. Cinnamomum zeylanicum is the botanical name for the purest and most potent form of cinnamon.