I just picked up this gimmick the other day and am astounded by its pure simplicity to use. This was a beautiful idea to come up with. The price is expensive (aprox. $40 U.S.) but is made to last a lifetime. It fits easily into your deck and can be made to work with any brand as well in just a few minutes.
Imagine being able to do the classic bill in lemon effect without having to switch the torn off corner. Another thing is that it allows you to tear a corner off of a card the exact same way each and every single time and with proper handling you can even have the spectator finish the tear to make the effect even stronger.
I purchased this at a lecture given by Dan Garrett and in his lecture notes and performance at the lecture he performed an amazing effect he came up with called "Torn and Re-born."
The effect: A card is "freely selected

Very strong magic able to be accomplished by minimal prep time and this wonderful gimmick. The gimmick also comes with a few routines (the one above is not included) and others can easily be imagined. I give this product a ten out of ten for strength of effects possible, quality for money, and the ease of use. If you don't have it I highly recommend it. Difficulty is nominal (with very little handling practice needed).
If there are any questions that I can answer without telling exactly what it is, or over some handling tips feel free to ask.
Brent