I would suggest checking with you current insurance..
Call the company you have, not the sales people, the claims people and ask them what your policy Coverage would cover. Give them examples.
Then do the same with the NRA one.. See if it's something you find a value.
I have had insurance in the past that I found out wouldn't cover my guns. (had, not now)
As a vet i have USAA and they just insure the value of everything. I have a dollar value of everything. They don't care what the items are. It's covered.
But, I always test the claims people, since when you need it, they are the ones that you are going to have to deal with.
Just my 2Cents.