Well I don't profess to know everything, but I do know that you can get those cards a LOT thinner. Unnoticeable from an ordinary playing card. If it is too thick for your eventual purpose, then please let me know via PM, and I may be able to help you.
Things to do with it? Hmmnnn. They can be used to steal cards from a deck, if you don't want to use sleight of hand, either via a tray or sealed box. I've seen various manufactured effects using them. Recently I saw a John Born lecture where he used this to produce 4, er hum, coins (with s***** ready for a matrix) from a deck. Very nice.
You could gaff a box, and add or lose a card easily, card under box (quite literally) or perhaps a prediction where you add it and thus will know exactly the bottomcard from a spectator shuffle? Maybe some sort of mental effect, they pick that card from a free choice

, all the cards are placed in a bag, you are completely blindfolded and are able to pick it out, then name it.