I bought this in place of a normal thumb drive. I once had a thumb drive that broke after a couple days of use and I lost all the data. Since then I have been using card readers, that way if I break the drive I still have the card. Also, in a couple of years when the SDHC cards get better SDHC card readers are upgradeable to 2 terabytes cards. It is a good system.
The round part of the card reader is almost the size of a dime and about 4 dimes thick and only 1.25 inches long. It is smaller then most of my keys. It fits even the tightest USB ports. It is so small, I don't even notice it on my key chain.
The only down side I could think of is that the USB port doesn't have a dust cover. Currently, I have not gotten any dirt in their but it could happen. Even if they did include one I wouldn't use it anyway.