Maybe somebody with a 997 si could answer a question for me, I am going to buy one of these units sometime this month and I am trying to decide which one to buy the unit with the nvb or without, heres the question what would be the benefit to me who only fishes local rivers, would be the nvb package, I dont understand this part of it. Any an all replys to this would be appreciated...........thanks people..........an good fishin