2013 Hyundai Elantra Ziebart rustproofing and undercoating

My car salesman is recommending the Ziebart rustproofing and undercoating for $400, 10 yr. Guarantee. I have always heard that extra rustproofing is a waste of money, but I my present 10-yr. Old car does some significant rusting around the wheel well. My salesman says that Ziebaart is an entirely different product than it was 10 yrs. Ago, and is worth the money. What do you think? I live in New York state, by the way, where we have a lot of snow, and therefore salt on the roads.