Possibly the Japanese model or a counterfeit, but it should be fine as an additional controller for when friends come around, so $20 may be worth the risk. It's from a farily reputable site but will likely be delivered from Hong Kong like DX.
They also have motion plus for about the same price.
Assuming this is the the same store their feedback score is over 200,000 on eBay:
http://myworld.ebay.com/hongkong.dragonext
http://myworld.ebay.com/au.electronics
Looks like the Official ones have 'Official' in the title.
I think these ones would be copies, but like you said; should be good if a mate comes round & doesn't know what's Official.