Summary: this is an awsome product I see everyone comlains about the price, however the product holds up to the name itself. When you buy a Canon product you know your getting a good quality. I have both a knock off hood and a Canon, and by far the Canon beats out the knock off in all areas. Good luck.
Pros: Better than off brands, Durable, Easy To Use, Good quality plastic, Lightweight, Reliable
Summary: After previously owning a Nikon with a similar lens hood that slipped on effortlessly, buying this lens hood for my Canon EOS Rebel XSI was a disappointing experience. The lens hood was for my 70 -300 Canon IS lens, it's a major hassle trying to get the lens hood to fit on my lens. The fit is not engineered well, I almost feel like the hood was NOT made to fit this lens. Nikon seems to have beaten Canon when it comes to accesories fitting together.
Summary: I use the lens hood whenever I am using the lens. It protects the end of the lens and blocks stray light. Little plastic grooves line up and the lens screws into place. I am still struggling with getting those grooves lined up perfectly. Lens also mounts backwards for easy storage. It does make the lens much longer, which might be a draw-back in tight situations.
Pros: Durable, Easy to Use, Improves Function, Lightweight