That treaty is potentially a huge threat to gun rights everywhere. Although I applaud the legislators and gun owners of NH for this bill, signing on to this treaty, which has long been a priority of Democrats, will make all action at the local level for naught. The treaty has to be ratified by the US Senate, and it's important to make sure that doesn't happen.
As others have said, the best thing the NRA can do is stay out of this matter and let the people and legislators of NH decide what they want to do.