[prydey]

It's not a legal requirement so if you fit it just to tick a box it's a waste of time. Ford do recommend using one though so for me it would depend on the actual weight you are towing and the ball weight.

It will smooth out the ride. It basically just stiffens up the connection so will minimise the porpoising effect a high ball load can give.

Don't try to compensate by adding weight rearwards on the trailer. Keep the weight over and/or just forward of the axles.

A wdh is what it says on the box. Weight distribution. Takes some weight off the rear axle and transfers it to the front axle and a small amount back to the trailer axle/s. When tensioning is important not to overdo it. Only tension it so the front guard is at most only 50% returned to its unladen height.