I just installed the standard TRD prius rear anti roll bar in my PiP. No issues. As others have reported, if your order the anti roll bar, it comes with the mounting hardware.
I installed that on my 2010 Gen III. The cornering is much flatter, but the steering gets a little squirelly since more input is needed through the turn to keep the line. Therefore I installed the Tanabe front strut tower brace yesterday, and it settled that whole issue entirely, even on and off throttle. So now I have normal car handling.
I have not noticed a huge change. On the other hand, I haven't been tring to corrner at the limits of cohesion. I think the car may be a bit more affected by crosswinds. If so, a friend suspects that rather than the car leaning as a result of wind, it now leans less and shifts around a bit more. The bar wasn't expensive. I put the rear wheels on wood 4x4's. The install was about an hour. The only amusing thing was it was impossible to torque the endlinks to spec as there was no way to get a torque wrench in the area. TRD won't admit that the bar will fit the PiP. My dealer said it probably would not fit. Fortunately, I suspected the suspension was pretty similar to the normal prius and the parts guy that I ordered it from conformed that, and said he would take back the bar if it didn't fit, and it was in good condition.
