I put these on last weekend, and I'm very happy. I did have to call to verify install information -- simple written instructions would have negated that. Other than that, installed easy, quality construction.
I have an early build E90, which had a sport pkg front strut mount that was soon revised. I put the old BMW performance suspension on, with heavier rear sway, keeping my sport pkg springs, and the revised front strut mounts (1/2" taller, surprise!) However, my former rack was gone, and the front fender-wheel gap looked bigger than the back.
Well, that wasn't going to work. So, after some research, I picked up these perches and out it came, again. Now the look to the car is back to what is was before, and with the new suspension, drives like a dream. More controlled, more feedback, absorbs bumps well, but quick rebound. And much less understeer. The new perches integrated perfectly.
I had an alignment done (because of all the other suspension work), but all front values could be adjusted to exactly mid-range.
From my experience:
The [perches] only act to raise the top mounting position of the spring thus bringing the car, and with it, the top of the strut shaft closer to the ground. Without lowering the bottom mount on the strut, your struts will be compressed more than without the caps. This decreases your suspension travel, increases chance of bottoming out and frequency of engaging secondary springs/foam bump stops, and makes the strut work in a different range than it was designed to work.
True. Struts are now compressed by 1/2", and you're 1/2" closer to bump stops. Which may be an issue with a completely stock suspension or if you have short springs. In my case, the performance suspension is designed to work with sport pkg or lowered performance springs, so I'm still within the strut's designed operation range, as are most aftermarket struts depending on what springs you are using.
Performance pkg comes with shorter bump stops for lowering springs, I used those. Anyone installing lowering springs, or in this case a lowering perch, should consider shorter bump stops based on the drop, there are several avail: Z3M, E90 M3, and presumably the one on mine. Inexpensive part of tuning your suspension.
Install tip: I put blue painters tape on the fender edge (protect the paint from the duct tape), and duct tape over that. The bolt studs from the strut mount will mark your paint if they contact.
I replaced the top nut on the strut, it is a lock nut with a metal collar, one time use only, and the stabilizer link to strut nut, since those are under constant movement. Cost, just a few dollars from dealer, piece of mind = priceless. Blue loctite on nuts to strut mount.