The brace stretching around the car laterally will, in theory, increase the rigidity of the chassis. The E82 has such a stiff chassis already, the affect will be minimal. I added one to my car and there was no discernible difference. I'd spend my money on a sway bar instead.
2006 BMW Z4M Roadster
Interlagos Blue/Sepang Bronze/Aluminum
Retired: '00 323i, '06 325Ci, '09 135i