a properly installed fork brace will do wonders for your front end. An improperly set up one will cause stichion and binding in the fork.
It has been ages since I owned a commando or even saw one but consider this: All of the 1970's japanese bikes came with them from the factory built into the front fender. I have ridden my cb750 without one and the front flex is unreal on stock forks.
It should be noted that there are two situations where the fork brace comes into play - uneven road surfaces and hard cornering. One of the hariest expriences I had was getting caught in a rain groove on the Long Island Expressway without a fork brace. The curvature of the road played hell with the front end even though the bike was mostly striaght up. When I went to move out of the grove the front end was really wiggly and flexing all different ways trying to get out. When cornering hard the fork brace works to keep the forks even, even though the forces involved want to compress one fork more than the other. On a cb750 the shocks are so pliable that it can throw the tire off camber which is really really bad.
On a set of properly setup race forks or carefully thought out street forks that are more rigid than stock and every inch has been gone over throughly I can see the reasoning that there would be too much rigidity (after a little flex is good) and that would make the fork less forgiving and more likely to lose traction. On a set of stock forks with little more than a service rebuild then the brace makes a difference.
off the cuff I would say that 60% of the aftermarket owner installed fork braces out there are setup improperly and are causing some form of stiction. whenever possible try to use one that uses the factory mounts (fender mounts) as you are less likely to screw it up.
Also I should note that there are two kinds of braces out there - slider braces and "tweak bars". Slider braces like what we have been talking about attach to the sliders and work on the dynamic part of the suspension. Tweak bars attach to the static chrome fork tubes and really just keep them from flexing in the case of extended forks. Really tweak bars don't do dick for your handeling on a stock bike, ro at least not enough as compared with a slider brace.
