So for anyone who's still on the fence... let me chime in. I can't speak for these bar in specific, but I can speak for the work of Dave and crew, and various sway bars on the Solstice GXP.
As many of you know I autocross on a national level (competed with DrJones and SnaponBob), and as such has sought out better handling out of car. I'd say the car, stock (the GXP has the base model upgraded sway bars as it's stock) understeers in corners. Upgrading to the Z0K sway bar in the rear helped the car move more towards neutral handling.
I'd still like a bit more sway bar, hence why I got in on these. My car (granted it's a bit more power than stock now) still can push a bit mid corner if you're on the gas too hard. I'd like to keep it planted a bit more to get the power to the ground sooner coming out of the corner. I'm looking forward to installing these and testing them out come spring.