Leaving aside the tyre rubbing on full lock issue for a moment, what exactly are the symptoms that they supposedly alleviate..?
I'm not a last minute or hard braker, so I've never felt the difference between the 4/4 (without) and the Roadster (with) although subjectively, the Roadster feels more planted under braking.
If you haven't got the bracing effect, I'd guess you'd experience a wander through the steering at peak braking which would lead on to all sorts of driver reactions.
Would this be the effect..?
That has been my experience with my 4/4. I owned it for a while before I fitted brake reaction bars, and your description of feeling more 'planted' under hard braking fits my experience exactly.
Do they make a massive difference under normal driving? No. Are they a must have? No. Is it a problem if they rub at full lock? No. But they are cheap and easy to fit, and could help stabilise the steering in a situation where one is braking very hard.
