This is a cheap imitation of a Nintendo item. I was quite happy to find it for half the price of the original. It looks very similar, but does not work as well. This item is meant as an add-on for the main Wii remote controller to enable certain games. The main problem is that the "Z" button on this unit malfunctions: sometimes it does not respond when pressed; sometimes it responds, but than spontaneously releases (despite the finger pressing on it). That makes games like Archery completely non-playable. In addition, even when it seems to work, it responds very slowly to the movement, which is rather annoying.
A curious note: it comes with the product insert and instructions for the main remote controller, which list all the items that "are included" (but are not) and says not a word about the Nunchuk. I was unpleasantly surprised to see amazon selling this. The item is very cheap and adding it to my cart earned me free shipping. Otherwise, I would have been seeking a full refund instead of stashing it in the old toys box.