So from what I gather, if I control 2, the effects are cumulative. If me and the opponent control 1 each, then the effects are basically negated.
Thanks for the reply.
If you each control a copy, the effects are greatly reduced, but not negated. Whenever something would suffer an odd amount of damage, (assuming optimal play) 1 less damage is dealt instead. That one point of damage can mean a lot (Bolts become Shocks, for a start).