Pretty cool. They are available on eBayPurchases made through these links may earn this site a commission from the eBay Partner Network too. Authenticity in either case?....I mean, you know...
I own one (as a part of the Mini Museum 1); it's pretty cool to have a piece of an actual Apollo spacecraft which has been around the moon and back (regardless of how minute it is). I think you can be quite confident about authenticity, the Mini Museum folks have a good reputation and solid documentation on the stuff they sell. The eBay version? I dunno.
Interesting idea, but a little too mini for me. Carrying this notion to the extreme, one could imagine someone selling genuine moon dust particles. Each would come with its own microscope for viewing.