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Cassia - the cinnamon most often used - is much more potent than Ceylon cinnamon, now known as Sri Lankan cinnamon, and often called "true" cinnamon, probably because it is in the genus Cinnamomum, and usually the species verum, though there are other, inferior species. The Mexican cinnamon, canella, is similar (mild, but not as thin barked), but a different species, Canella winterana, native to the new world, and one of those things that the made some of the first visitors think that they had circled the world - they had found cinnamon!
I use the Ceylon cinnamon in Mexican cooking, as well as many Indian, and other foods, in which I don't want an overwhelming cinnamon taste. That is what turned me off to most of the Indian foods (and a lot of Middle eastern foods), in which the spice mixes they used would have raw cassia in them. However, making it myself, using the milder, Ceylon cinnamon, and toasting it, along with the rest of the spices, makes the flavors wonderful, with nothing overpowering. And the thinness of the Ceylon cinnamon makes it easy to break up, to toss around in the skillet, while the cassia can be incredibly hard - unless you buy it in those bits and pieces, the way they sell them in Indian markets, some of the stick can't be broken, and I know someone that broke a blade in a spice grinder on one.
I have written on some of my jars, for when I'm using the bits and pieces, "2-3 grams/inch". That's about what I found average for both cassia and the Ceylon cinnamon, and some can be much heavier or lighter.