From my understanding they don't. I know a couple people on here were going to test similar theories, so you might do a search for those threads and see all the weird ways people say the can sex eggs.
I was just checking out the listing again and noticed they have sold 21 of them. We have a term here for those people here. I will be nice though and keep my pie hole shut.
While they are at it they should market the magic 8 ball chicken sexer..... I suspect it is just as effective. Once you're done sexing your eggs you can tackle the other difficult questions in your life with certain certainty!