Coming from GameFAQs...
Just wanted to give a heads up on people buying this. The product is great and it works but: Nyko accidentally shipped boxes with the 3DS cable in the Wii U box. So make sure you check the box and see if it has the right Wii U connector cable in it.
Lik the person says, just make sure you check the box before you actually purchase the item. A 3DS cable is nice, but it won't do you much help with the Wii U! Thanks to Whatami for the heads up!
UPDATE - Nyko says they're "... moving swiftly to rectify the issue."