See this thread on e90 post. Includes impressions/review of the inserts and installation tips. As mentioned there seems to be no need to remove the old bushings and thus, the subframe doesn't need much clearance. Just enough to wiggle the bushing in. It seems like a great alternative, and a better project to tackle DIY. I'm waiting to hear the next update on that thread, and also some others impressions to see if there is a significant improvement with the inserts.