I am just curious. Why a cardreader. What about connecting your camera through USB to your PC? I do that with my 7D, goes fast using the EOS Utility. (Cards Sandisk 60MB and Transcend 600x)
For me, mostly because it's slow (compared to USB 3.0 or FireWire 800). I find the transfer rate important, since I copy & paste all images twice (normal storage + backup).
Also, there are times when you want to keep shooting (with a second card) while the first card is being copied to the hard drive. So you need the camera to be not-occupied.
And also, I don't want to waste battery power (even if it's not a big drain) for transferring files to the computer.
These are enough reasons for me to use a card reader rather than attaching the camera directly.