Third Party Lens Hoods
The difference between Canon and third party lens hoods.
Top hood is a third party EW-83E replacement, the bottom hood is a Canon EW-73B. This photo illustrates the effect of the felt on the inside of the Canon hood - it does not reflect light whereas the smooth surface of the third party hood does.
Does this justify paying 2-3x as much for the hood? Hard to say... I'd need to purchase a third party EW-73B and test them! But given the difference I believe the third party hoods should cost far less than they do, so it's a choice between being ripped off by Canon or a nameless trademe seller.