Re: that eBay listing, it says 3M in the title, however that refers to the length "3M x 20MM", no where in the listing does it say it is "3M" brand and if you look at the photos of the roll, the 3 and M letters are strangely not pictured together, unlike the Amazon listing which clearly shows the 3M branding.
I could be wrong, but it looks like the ebay listing is for an inferior copy, hence the cheap price.