When throwing away personal documents I used to almost exclusively use the shredder. However most letters that are sent to me (including junk mail) only contain my name in one or two places, and shredding them is rather a waste of electricity and time - not to mention the annoyance factor when the shredding mechanism on the machine gets clogged.
These scissors are a great alternative, and are really simple and easy to use. I am concerned about the photo showing them being used to cut credit cards though, as it's difficult enough using them on thin card. One star off for that, as I think it's misleading.