Zen's right, Edge is not really an upgrade for most 360 users. Edge has balistics curve for ST's, but won't have the smart-advanced features, the ability to make a standard translator, or an LCD screen.
If you mostly just use ST's, there will be no difference it actual performance between the two on the Xbox. If you are one of the really hardcore guys that knows how to make a ballistics curve, then getting an Edge may be worth it to you.