The magic trick itself can be pretty useful, but usually people will suspect what's going on. It's nice to have just to have though. Plus, if you carry it around and ever need to flip a coin you'll always win. Have them call it in the air. If they say tails, great! If they say heads, just cover it, and slowly turn it over to show heads on the bottom. If you act excited, they won't suspect that it's double sided.