I've have the full SPL catalog on my Z.
Have over 15,000 miles on the front suspension. No issues there. In the rear. When I installed the SPL sub-frame bushings. That's when I picked up some increased noise from the rear. Mostly from the diff.
From over the years of being on this forum. I have yet see anyone have issues with the SPL parts. Lot of issues with other makers of suspension parts tho.