I'd be up for a group buy 100%
As for someone who has one, Steve (aka tk421) on the forums has one. I've been in his car with it, and it seemed to stiffen things up quite a bit and also seemed to lessen the amount of rattles experienced in his NB8A.
I didn't notice any massive understeer when we went for a drive. Everything seemed like it was stiffened up much like the improvement you get from a front strut brace, but all over. We were flying through Galston Gorge, but admittedly my attention was being held by the performance of the supercharger rather than how the car cornered
Another point to note is that he has the factory Bilstein suspension in his car which may also contribute to the overall feel of the car and also help in rattle reduction, so I don't know how much of the suspension/rattle reduction can be attributable to the brace.
Fitment wise, I seem to remember that carpet needs to come up so holes can be drilled for the mounting of it. Perhaps if a group buy is organised, a group installation at Mania might be a good idea, much like the BD bars?
How long until the sale is over? If you want to group buy and the sale ends quick, we'll need to act fairly fast. Shipping will also be an interesting one because these things aren't exactly small and lightweight.