Wiikey Fusion Clones
Just found out that there are Wiikey Fusion clones out and for those who try to register and get that the serial is registered to another user. The only thing you can do is contact the place you bought it from as Wiikey support will tell you the same.
Doesn't neccessarily mean a clone.
Example would be that someone ordered it. Registered the key during the time when it came with firmware 1.2 or less. Found it didn't work with to well as advertised and returned it in the 2 week period of ordering it. The serial being still registered to that email, the wiikey fusion gets resold to someone else when it passes any checks by the reseller for defects from the previous owner. In this example, the wiikey site currently has no deregister methods of taking out any keys when returning a product to a vendor.
or it could be like a clone like you said.