I tested the molds with the same canele batch.
The caneles being baked in the convection oven. You can see how the batter "rises" more evenly in the copper molds, and there's already some color on the top as well.
Fresh out the oven. The batter "shrinkage" is more even in the copper molds.
Wow! See the differences?
I say the copper molds are totally worth it.