I've got totally standard suspension and had the handling kit put on a couple of months ago. I didn't get the front camber bolt though and the back ones aren't on yet as I'm gettin them put on when I get my Tein super streets fitted hopefully later this month (as they come with adjustable top mounts). I also have Whiteline front and rear strut braces.
Tbh, from what people have said I was expectin a massive difference but it was more subtle. It is noticeable though. It feels tighter round corners, there is less lift under acceleration and considerably less dive under braking wiich makes the car feel much sturdier before corners.
It still understeers a fair bit under acceleration or round very fast corners but a lot less than it used too and I have the ARB set on the middle of 3 settings so could tighten up the rear even more (but don't wanna spin or owt). I think a lot of this will be sorted when the coilovers go on as there'll be less body roll so more weight on the inside wheels so if yours is already lowered you'll get this benifit.
The ultimate way to get rid of the dreaded understeer though is apparently the bumpsteer kit made by Power Station and distributed by Whiteline, which I'll be gettin put on sometime in the not too distant future hopefully.
Handlin is definately the way to go, especially round here in the lakes
Hope that helps you a bit.
Chris