Got the H&R ARBs installed today. Can't see much difference between stock front one and the H&R but for the rear, the H&R is so much thicker, 20mm v 13mm.
After the installation It is evident that body roll has been greatly reduced. There is a slight bit of body roll only, guess a portion of that can be dialed out with a new set of coil overs. With the thicker rear bar, the bias is now obviously stiffer for the back and the car's understeer is no longer present. Entering corners, you will feel that the car is most eager to turn in. For me it felt unnerving at higher speeds, guess I need to get used to that and adapt accordingly.
It's now a pleasure when driving on twisty roads. A balanced chassis, hardly any body roll, the lack of understeer ... This is a very worthwhile mod to a BMW.