I have a set waiting to be installed. The general impression I've gotten on this forum and FB groups is they do reduce body roll and some of the looseness in the rear - but if you could only do ONE mod, sway bars wil make a bigger difference. I personally got them because they might keep the car in alignment longer
They made a difference for me. Doesn’t feel loose when you hit bumps. Feels more solid (than sways alone). I got the collars added a month or so after my springs/sways. So I have compared the difference. As a side note, I was diving on Saturday and someone entered my lane (came in my blind spot on the passenger side I was in the left lane and I saw him at the last second before he hit me). The car handled like a champ. Total control. I was able to quickly do a quick maneuver and maintain the road. My wife (riding with me in the passenger seat) who has gone up to Mid-Ohio Racetrack and took their racing classes was impressed with the car’s handling. In the past (after I changed the suspension and before this day), she had felt I lost something comfort wise when I switched (she noticed it when we went on longer trips). After Saturday, she was sold on the change and realized the Suspension change (springs/sways, and the ATQ collards) probably saved us from a serious if not fatal wreck.