The fact that it is not Nation wide or at least offered by others should be a clue.
When I bought our first TT we insure it for what it cost us, not the replacement value, for four years. I wanted my money back if I drove off a cliff. :)
It was costly but we had some serious road damage repaired because they did not want to replace it. When that policy expired the value of the TT dropped so we switched to an adder on our car insurance.
I would pass on any "forever" guarantee on an object whose value drops like a stone in water.