Either before use or on the very first attempt to insert a CF card, a pin bent, needing fixing back into place. I managed to do that, but when I use it now, inserting it into my laptop with the CF card draws power in excess of USB specs leading to the error: 'Because a USB device was drawing too much power from your computer, one or more of your USB devices have been disabled.'
Thought it would be a good idea to go for a brand name card reader for a change, as the others tend to fail after a while. Turns out I got absolutely no use out of it whatsoever, and that it was just a waste of £20. Hooray!