It fits the Canon EF-S 18-55 mm IS Lens, and I didn't notice any shadowing even at 18mm. With the UV filter on though, the hood moves a few mm forward from the lens, and the round bit inside the hood gets in the way, causing the corners of the picture to get dark. I don't think this is because of the petals, because they would appear on the sides.
Personally I regret buying this hood and would not recommend it to anyone to use with the EF-S 18-55 mm IS Lens, for the reasons explained in the product description which somehow I seem to have missed reading. The front side of this lens rotates while focusing and so does the hood. Other reviewer said he/she uses the locking ring to rotate the hood; so do I for now, unfortunately, but that ring is to be used for tightening it onto the lens/filter, not to keep the hood straight when focusing.
I will have to buy a different one soon.