The nerfs will keep you from hooking the tree in most cases. However, if you are carrying good speed through the trees and clip the side enough that the nerf makes contact hard, it will still kick the rear to the side a bit. Rocketman once hit a tree on his left where the nerf did it's job too well, deflected him to the right and into another tree completely collapsing the right side nerf bar into the side panel.
My nerf bars show the signs of several tree kisses and I'm sure have saved some serious wear and tear on the rear axles and control arms.
The only suggestion I would make is to consider purchasing the ATVR style nerf bars that incorporates a truss type design along the bottom, parallel to the ground. They are much more rigid and absorb a hit more evenly down the entire length of the nerf.
