Needs 3 x AA battery's to power it on with a switch on the side. Its usefull when the main electricity in the house goes down or go out camping as emergency lighting. Because its led powered it stays on for a long time.
Instead of take your main plug cable out and in all the time. Just plug in this gadget and press on and off. In the long run it saves you some money and with that money you can buy yourself a hamburger or more. :)
Sometimes when your laptop doenst have a sd card reader it can be very problematic. Small Usb card reader is easy to use, because its plug and play. For me it worked for a macbook as wel windows.
So get 1 because its small and cheap to get.