After installing the the H&R sway bars, there was an instant improvement, noticeable even in everyday driving. The car felt much flatter through the corners, the front end seemed much more sensitive ie more willing to turn in, to such a great extent that I had to consciously modify my driving style by being much more gentle with my inputs. But after a week, I quickly became accustomed to it, and don't have to "think" about my steering inputs.
Bear in mind, you can set the level of stiffness of the bars by connecting up the end link to different holes at the ends of the bars, and thereby affect the cars tendency to understeer or oversteer. I set mine up to increase oversteer, (in fact to maximum oversteer), FULL SOFT at the front, and FULL STIFF at the rear, as I've always felt that the 330ci is a heavy car, set up for safe understeer and not so willing to turn in. However after a few weeks, I set the front to its middle setting.
Here's a link to UUC's website that explains sway bar setup which i found useful:
Here's a few DIYs i found useful. The first is an excellent video by Bav Auto, and the second link is useful in showing how to disconnenct the end link with the help of the factory vice locking pliers.
My tips for the install:
(1) Jack up both sides of the car, so both wheels are off the ground. DO NOT jack up only one side and remove and install the bar. For the front bar I only jacked up the right wheel, and managed to swap out the bar with the left wheel still on the ground. After completing the install there was a little knocking coming from the front left especially as I went over bumps in the road. I think with one side of the suspension/bar loaded and one side unloaded this probably caused and uneven and excess load/pressure being place on the left end link and caused it to fail. I replaced it with new Lemforder end link and all was good.
(2) For the rear bar all the DIYs seem to show the removal of the end link from below, but it is incredibly tight access that way, and I think it would be very frustrating. Instead I jacked up the rear of the car and placed it on jack stands, and removed both rear wheels. The picture below shows how much easier it is to get access to the end link bolts that sit above the rear wishbone: