I have the Nagisa Auto ones and they're maybe 2 pounds at the most.

Is it safe to assume that your Dad has little to no experience with unibody or macpherson strut cars? The entire front of the car is suspended by the strut tops. When you take a turn, the strut tries to force the strut tower inwards and back. The strut tower takes care of the inward motion, but the fender brace works against the backwards force. Also in the 3rd dimension, weight suspended in the middle of the car will try to fold the car in half by the firewall. The fender brace will help here too, but the frame will absorb most of this force vector.

The S13 isn't exactly a BMW 5-series. You could brace just about anything and make a difference if you have stiff suspension.