i've seen those on ebay too and also wondered about them. i did a search a while ago and i believe it was mainly marketed in japan. i also found a website that was selling them for pretty cheap. click the link and go about half way down the page.

http://www.ffo-tackle.com/ProductDirectory.cfm?PassProdCat2=Freshwater%20Soft%20Baits&PassProdCat1=Baits&SearchLevel=3