I have a very rare Rubik's Magic Snake for sale on Ebay.co.uk at the moment, but don't really know much about!
It's still sealed in the original packaging, and has no mention of the name Rubik's on it, it says 'Patent Pending' and is not dated, so is presumed to be 1981.
I searched the internet and only found one that was sold in it's original ball, and there was no mention of if it was branded Rubik's or not - the reason for this is probably because you have to rip the label down the middle to get into it!
If your interested go take a look! 2 days left.