The second dealer is right. The fact that the chains hang at an angle has no effect in there effectiveness. Yes it does increase the tension on the chains by the trigonometric function of that angle but not to worry. Those chains will carry many times the load you are going to apply.
I would suggest you look at a sway control bar set up rather than the friction plate system. The friction plate system is a pain in the butt.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles