Just to put this into perspective, it is a very nice effect and something that is new on the market but, I've personally tried and used these cards, and it is not as great as it seems.
It is new and innovative and very cool but, when you rub the spades it doesn't become fully invisible...as well some of the hearts are upside down, and they change with barely any heat so keeping it in a deck and handling it may change it. And when they change, you can tell that it's not actually hearts jsut due to the fact some of the ink just fades and doesn't completely change (mainly the "tails" of the spades.)
They are definetely cool and innovative but, I think a more careful process should have been done to create them.
-RA69