Handheld models can only shred a sheet or two at a time, but they can be good enough for a single person or small family.
Make sure to keep the wastebasket empty. For a shredder to work efficiently, the shredded paper needs to be able to drop freely into the wastebasket below.
The opening of a shredder can affect its capacity, because if it is small, you will need to fold the paper to fit it into the machine.