If amicus briefs were not effective, no group would go to the trouble and expense of preparing them and filing them. The fact that every side of an argument files briefs shows that they are important. It's hard to know for sure if a brief does any good. However, it is always better to be in the fight than to watch from the sidelines.
This is a chance to add our voice to the chorus of voices the Court will hear. It is an opportunity to be sure the Justices get as much information on our side as they get from the radical anti-Bill of Rights side. It may be our best chance of restoring our Second Amendment rights. We may not get another chance if the Court goes the wrong way.