I read a review of someone who installed these on their 335 (I think). They concluded these were a good alternative, especially if you were doing the job yourself. The rear subframe did not need to be fully dropped, and the labor time was 3-4 hours instead of 6-7, but they also said that if you were paying a shop to do this, you might as well pay for the extra labor and have the actual M3 bushings installed, as you're not saving that much if you're paying a shop to install the inserts.
These DO look like a good alternative. I'm having the M3 bushings installed today, not cheap at around a Grand.