My 8 year old has some but I honestly don't know much about them.
He showed me how they opened up. The cards have some type of magnet in them and when the balls are placed on the card the ball opens up to reveal some type of monster.
It looks like there is a game that goes along with it but my son seems more interested in watching them open up.
I suspect it is just a passing fad. He seemed interested for a few days but haven't really seen him play with them much lately.
"The farther we go, the more the ultimate explanation recedes from us, and all we have left is faith."