As someone who is from Ceylon (Sri Lanka), I'd say to be careful of the most commercially available cinnamon that are meant to be used with food and tea too, because they may be flavored to dial down the otherwise strong taste/aroma of cinnamon.

I know because one of my friends has a cinnamon farm, and what he makes at his place is nothing compared to the cinnamon I could buy from supermarkets when I was living in the Netherlands. Look for Sri Lankan markets if you are looking for unaltered stuff.