Poita, the USB adapter should allow it to upload from a camera, but not much else. Like Andrew I have the Apple SD card reader, no issues apart from iOS obviously not checking to see if there is enough spare storage.
SD reader works fine, USB only has limited support in iOS and will not work on anything that requires power from a USB port such as a USB stick, really only for USB cameras that have their own battery.
I already have the genuine one. It works fine for me on my SD cards, USB keyboard, USB joypad and USB mic. Oddly it works with my Microsoft keyboard and not my old apple one!
I'm grabbing the $7 one just to see if it works as well as the official unit.