Re: choice band
It raises attack moves to 1.5x power, or by 50%. So, if you give it to a Heracross, that say has 380 attack, it's attack will then be this: 380/2 = 190. 380+ 190 = 570.
The same equation applies for any pokemon. The only downside to this is that you can only use one move until you switch out. Then when you switch back in, you can use a different move.