I bought an official iriver case for my Girlfriend's iRiver, it is a bit like a plastic wallet. I am not especially impressed with it.
Were it given away free with the iRiver it would be adequate, it certainly is enough to keep the iriver protected fromdamage etc.
Given, however, that it's a paid for extra that you seem to have to scour the earth for it's not so hot.
Have not seen iGadgitz one though so cannot give a direct comparison.