There are basically two types of 'cinnamon" for sale, real Cinnamon and Cassia.
Most of the "cinnamon" for sale to supermarket shoppers is Cassia.
However the discriminate cook knows that the taste of Cassia is less delicate and complex than the taste of real Cinnamon.
You can tell the difference when you buy the sticks. Cassia sticks are thick and dark, real cinnamon sticks are made of thinner bark and are lighter. Once you have seen them once you can recognize them.
If you buy your cinnamon in powder you can find out which is which. Guess how?
Cinnamon and Cassia both contain coumarin, which is supposed to be bad for you in high doses because its destroys the liver. The use of Cassia is restricted in Europe for that reason. Cassia contains a lot of coumarin, while there is very little in real cinnamon.
I never had a problem with cinnamon ingestion, apart from the fact that if you suddenly take a big amount of cinnamon, it will kill a big fat load of Candida in your gut with subsequent Herx reaction.
So most probably apart from the effect of cinnamon on insulin resistance, you would have an effect of decreased insulin resistance because you lower the candida population.