I'll add my two cents man.
From my tests, I didn't like what I saw on the majority of what I used it on, UNLESS I got it right from the start. If I got it, and then tuned it, then the tune worked around 'whatever it does'. But any car I've already tuned, (*this is important), adding this threw off the feel of the ride. *however, if after the tune, something doesn't "feel" right about your car, maybe your tuning it, and the rides a little shakey and no matter what you change it doesn't effect it, try this.
Case in point;
One of my grind cars is the BMW Z4 M Coupe. Wonderful car, but no matter what I did to it, it felt like I needed to change something, but I couldn't quite figure out what. So I got the rigitidy improvement and nailed it. Bugs gone, and the rides very tuned now.
I still say, use it as a last resort. You don't want to have to buy 2 of every car if you don't like it, lol.