Alot of people on here will say they're a waste of money and don't work but,
I have a rear strut brace and I noticed a difference straight away,
when I first ditched the back seats and spare wheel the back became alot lighter, I got use to how it felt but when I fitted the rear brace,
I took the car through a series of bends I drove every day and the back felt more stable and less spongy,
this could just be because the rubber top mounts on the rear dampers were softer than others
and the brace stops them from moving around too much.
I also met a member at a meet that had a front strut brace fitted and asked him if it made a real
difference, he said it did and he went on regular track days so he drove his car hard quite often.
But hey, everyone feels different things in different cars.