I've been using the U.S. quarter Gerti and it's a winner. The DVD is well done with thorough explanations and extra routines.

For the basic lie detector routine, there really isn't anything to learn except a routine. The better the routine, the stronger the impact.

I ask if they have a quarter ( the one time someone didn't, I gave them one to use ) I take a few coins from my pocket. I have a penny, nickel, dime and 3 quarters ( one of them is Gerti ).

My gimmick has my initials pre-signed. When I take the change from my pocket ( I simply make an adjustment so my initials aren't showing.

I have them initial their quarter and then I pretend to initial mine. They take both quarters and I turn my back, holding out my hand for them to place one of the coins into my hand.

That's it. You know which coin you have. The rest is acting/routining.

People are gobsmacked that you can know which quarter is where based on their tells. I'll carry this with me, always!

The secret is just what I suspected, so... yeah. I can't use any available currencies in my country, I will have to make one for myself. With all these, The gimmick is useless, the method is eh, ok... so I would be much happier now if it was only 10$.
But if you live in a country where you can use the gimmick, buy it for 20$. I don't feel it too strong by itself, but it's a clever idea, and you can use the method combined with other things to put together a great rouitine.

The gimmick is a good idea ! It's really simple to use and almost totally invisible.
But be careful : do not pay your daily newspaper with the gimmick ! ;)