Originally Posted by yayo
Does it make any difference using a class 10 SD card versus using a class 4?
I don't think so. Class 4 should be perfectly fine for a "slow" device such as an ebook reader. Class 10 would be needed for a camcorder of camera needing high bit rates for writing on the SD.
Myself, I chose a Class 10 SD for the M92 so that I would be able to use it in such a device (camera or camcorder) in the future, if needed.