I installed them on a Performance Y recently. Unfortunately, the results are not what we expected. We were hoping the car would have a slightly lower appearance and a slightly sporty feel (taking exit ramps faster, etc). We didn't expect a smoother ride because we were hoping for a sportier ride.
We took one of our two Performance Y's to the shop UPP recommended that was about an hour away. The installation price was more than double what UPP said to expect when I asked UPP how much it would cost to install before I ordered the springs (they said about $300, it cost $791...the other place I called said $1100). So in total, I paid about $1200.
When we picked up the car, we couldn't see any difference in the height. We thought when we parked it next to our other Performance Y we would. Unfortunately, we didn't. I can put 3 fingers in between the front driver's side wheel well with a tiny, tiny bit of wiggle room on the non-lowered Y, I put 3 fingers somewhat tightly on the lowered Y.
Next driving, neither my wife nor I could notice any difference what so ever in the sportiness of the car. With that being said, we aren't track people, just sports car people who hoped to make the Performance Y a tiny bit sportier, as far as handling goes. We also haven't noticed the ride being any smoother over bumps/pot holes (not that we expected it to). If you track your Y, you may notice a tiny difference, but we don't.
With all this being said, UPP has checked in several times and seems genuinely interested in our feedback and trying to resolve our concerns. I'm going to work with them to do whatever we can to hopefully improve the situation for us and future buyers. I know UPP has a great reputation and I fully expect good things in the future. I hope to come back to this thread in the future to say what an awesome job they did making a bad situation a good one.