I am on the fence but leaning against the charter. No one has come out and specifically differentiated it from the current form of governance. Where is the benefit to Merrimack citizens?

You asked what is the benefit to Merrimack Citizens, here are a few thoughts on that:
1.) The current BOS is made up of 5 members. The proposed Charter changes the count of the Governing Board to 7 Town Councilors.
This means it is more likely people elected to the Council will reflect your views of how the Town should operate. These people are elected at-large so they do not necessarily have to live in your neighborhood.
You have greater representation on the Governing Board and it is less likely a few can monopolize the proceeding of the Board/Council.
2.) The Council is required to make time to hear your concerns at each regular meeting. This has been the custom lately, but now it is required.
3.) The Council can be forced to act. Through Article 10 the citizens have the power to force the Council to act and have the power to overturn a Council action. Today, a citizen or group of citizens can complain in public or private, but they cannot force the Council to act or overturn the Council. Your only recourse is to vote them out of office after their 3 years are up.
With the proposed Charter, a group of 50 can petition for a change, petition for an ordinance, petition for something to happen. The number is seen by some to be high at 50, but remember you want the Council to do something and there are over 17000+ registered voters where a vote of the Voters would require about 4000 votes in favor based on the last Town election.
If the group is larger at 500, it can actually force their idea, ordinance, measure, etc. to be placed on the Warrant. Yes, 500 is high, but the Council would have to be really ignorant not to acknowledge the 500 signers. Again, 500 of 17000+ registered voters where about 4000 (based on the last Town election) would have to agree at the Ballot is maybe not that large a number.
Then there is referendum as well where the citizens can overturn a Council action.
We currently have none of these options guaranteed in our current form of government.
4.) The Charter enforces the Ethics ordinance by putting it in the Charter. This means the Council cannot do away with the Ethics provision, only an amended or revised Charter can do this.
5.) The Charter creates an open process for the adoption of ordinances. It includes multiple hearings, postings, and a waiting period before it can be enacted.
Most people do not realize this now but the BOS can now enact ordinances without a vote of the citizens. They only need a single Public Hearing and can act immediately after the hearing. The exception to this is zoning ordinances. The BOS could have enacted the noise, nuisance, or bus ordinances we saw at this years Deliberative Session on their own if they chose to do it.
6.) The Charter enforces a non-inference provision so a Councilor cannot go into Town Government and administer the Town on their own.
7.) The Charter keeps the final Budget vote in the hands of the Voters.
8.) The Charter allows for adjustments (amendments/revisions) as time goes on. Currently, our government can only be changed by a vote of the Legislature and Governor in Concord.
9.) The Charter creates a standard “posting” form so that Public Hearings and other items are more likely to be seen by the citizens. If the citizens can see it, they can know what is happening and not be surprised.
10.) The Charter forces the Council to review all Town Ordinances on a regular basis so they remain applicable and relevant.
11.) The Charter forces an Administrative Code so everyone can accurately understand how our Town Government (Town Hall) is supposed to devised, how they act, how they get paid, etc. The Town has an Administrative Code today, but it is not up to date and does not reflect today’s Town Hall.
12.) The Charter requires the Council to post agendas in a timely manner.
There are others, I hope you get a chance to review the Comparison as well.