I used the IPD kit, and it took considerable fiddling to get it to hold the panel solidly so that it didn't rattle, and the third brake light was tight against the back window (to prevent annoying red glow in the mirror when braking at night) and then the gap between the top edge of the panel and the glass was larger than I would have liked. (but at least it was finally quiet...)

On another car I dismantled, I found a kit had already been installed, but the plastic clips had actually torn through the thin sheet metal of the repair pieces. The whole thing is just a bad design, and unfortunately, it carried over pretty much unchanged onto the 850 wagon.