They reduce full shock travel while putting more pressure on the oem bumpstops to compress. I cut the oem bumpstops in half and start with 3 fk's on each rear. Anymore will end up causing the vehicle weight sitting on all the bumpstops, this will hinder max drop on your coilovers. This is the ghetto way of minimizing rub esp full load/high speed. Just jack up the rear and jam them under the oem bumpstops, literally takes 20 secs to do on each rear. You can not even tell they are on while normal driving.
So unless you want to shave fenders or increase coil rates to minimize rubbing this will be a cheap alternative. Ive recommend them to at least over 20-30 ppl and sent them all over to Eric or Tam at supreme powers (vendor here). Those who have installed them can vouche for it. As ive recommended them to everyone running minor stretch/flush/poke with aggressive width/offsets 10+25/10.5 +22/11-12 so on.
btw....Alen E90 is the e90post angel, just sayin: